h.md

H

Hackathon : A Sprint-like event, and often one in which computer programmers and others involved in software development, including graphic designers, interface designers, project managers, domain experts, and others collaborate intensively on software projects. The goal of a hackathon is to create functioning software or hardware by the end of the event. †

Hacker : Any skilled computer expert that uses their technical knowledge to overcome a problem. While “hacker” can refer to any skilled computer programmer, the term has become associated in popular culture with a “security hacker,” someone who, with their technical knowledge, uses bugs or exploits to break into computer systems. †

Haml/HAML : → HTML Abstraction Markup Language

Handlebars : A templating language. Handlebars templates use expressions in the form of {{, content, }}, resembling handlebars. ℹ︎ handlebarsjs.com

Hard reset : An early 2000s reset “style sheet” that resets the margins and paddings of all elements (* { margin: 0; padding: 0; }).

Hardware security module : A physical computing device that safeguards and manages digital keys and that performs encryption and decryption for digital signatures, authentication, and other cryptographic functions. Hardware security modules traditionally come in the form of a plug-in card or an external device that attaches directly to a computer or network server. †

Hash : → Number sign

Hash function : Any function that can be used to map data of arbitrary size to fixed-size values. The values returned by a hash function are called hash values, hash codes, digests, or simply hashes. The values are used to index a fixed-size table called a hash table. Use of a hash function to index a hash table is called hashing or scatter storage addressing. Hash functions and their associated hash tables are used in data storage and retrieval applications to access data in a small and nearly constant time per retrieval, and storage space only fractionally greater than the total space required for the data or records themselves. Hashing is a computationally and storage-efficient form of data access. †

Hash table : A data structure that implements an associative array abstract data type, a structure that can map keys to values. A hash table uses a hash function to compute an index, also called a hash code, into an array of buckets or slots, from which the desired value can be found. In many situations, hash tables turn out to be more efficient than search trees or any other table lookup structure. For this reason, they are widely used in many kinds of computer software, particularly for associative arrays, database indexing, caches, and sets. †

Hash-Based Message Authentication Code : A specific type of message authentication code (MAC) involving a cryptographic hash function and a secret cryptographic key. An HMAC can provide digital signatures using a shared secret instead of public key encryption. It trades off the need for a complex public key infrastructure by delegating the key exchange to the communicating parties, who are responsible for establishing and using a trusted channel to agree on the key prior to communication. †

Hashbang : → Shebang

Hashtag : A type of metadata tag used on social networks such as Twitter and other microblogging services. It lets users apply dynamic, user-generated tagging that helps other users easily find messages with a specific theme or content. Users create and use hashtags by placing an octothorpe (#, also called a number sign, or pound sign) usually in front of a word or unspaced phrase in a message. Searching for that hashtag yields each message that someone has tagged with it. A hashtag archive is consequently collected into a single stream under the same hashtag. †

hasLayout : A peculiarity in Internet Explorer ≤8 that influences how page elements are drawn or interact. Though some elements “automatically” “have layout,” hasLayout can also be forced by particular CSS properties and declarations. ℹ︎ is.gd/KcpK3B

HCI : → Human-Computer Interaction

HDD : → Hypothesis-Driven Development

Head-of-line blocking : A performance-limiting phenomenon that occurs when a line of packets is held up by the first packet. Examples include input buffered network switches, out-of-order delivery, and multiple requests in HTTP pipelining. †

Heading content : Content that defines the header of a section (whether explicitly marked up using sectioning content elements, or implied by the heading content itself), marked up through the h1, h2, h3, h4, h5, h6, and hgroup elements. §

Headless : Software capable of working without a graphical user interface. †

Health check : Typically recurring, automated requests to confirm that a machine or application is available and functional.

HEIC : → High Efficiency Image Coding

HEIF : → High Efficiency Image File Format

Helper class : In software development (object-oriented programming), a class that is used to assist in providing some functionality, which is not the main goal of the application or class in which it is used. An instance of a helper class is called a helper object. † : In web development (CSS), a class that has no functional bearing and carries no particular meaning (like .aux or .alt) but serves as an intentional hook for complementary or alternative styling.

Heterogenous migration : A migration where source and target systems are different, as with different database engines.

Hex : → Hexadecimal

Hex triplet : A six-digit, three-byte hexadecimal number used in HTML, CSS, SVG, and other computing applications to represent colors. The bytes represent the red, green, and blue components of the color. Each byte represents a number in the range 00 to FF (in hexadecimal notation), or 0 to 255 in decimal notation. This represents the least (0) to the most (255) intensity of each of the color components. Thus web colors specify colors in the 24-bit RGB color scheme. The hex triplet is formed by concatenating three bytes in hexadecimal notation, in the following order: byte 1—red value (color type red); byte 2—green value (color type green); and byte 3—blue value (color type blue). †

Hexadecimal : A positional system that represents numbers using a base of 16. Unlike the common way of representing numbers with 10 symbols, hexadecimal uses 16 distinct symbols, most often the symbols “0”–“9” to represent values 0–9, and “A”–“F” (or alternatively “a”–“f”) to represent values 10–15. †

Hick’s Law : A model describing the time it takes for a person to make a decision as a result of the possible choices they have, asserting that increasing the number of choices will increase decision time logarithmically. Hick’s Law assesses cognitive information capacity in choice reaction experiments. The amount of time taken to process a certain amount of bits in the Hick-Hyman law is known as the rate of gain of information. †

Hick-Hyman Law : → Hick’s Law

Hidden Web : → Deep Web

High Efficiency Image Coding : → High Efficiency Image File Format

High Efficiency Image File Format : A file format for individual images and image sequences. It was developed by the Moving Picture Experts Group (MPEG) and is defined by MPEG-H Part 12 (ISO/IEC 23008-12). The MPEG group claims that twice as much information can be stored in a HEIF image as in a JPEG image of the same size, resulting in a better quality image. HEIF also supports animation, and is capable of storing more information than an animated GIF at a small fraction of the size. †

Higher-order component : A function that takes a component and returns a new component.

Higher-order function : A function that either takes one or more functions as arguments (procedural parameters) or that returns a function as its result. †

HIP : → Host Identity Protocol

Hit : A request to a web server for a file (such as a web page, image, script, or style sheet). There may be many hits per page view since an HTML page can contain multiple files, such as images. †

HITS : → Hyperlink-Induced Topic Search

HMAC : → Hash-Based Message Authentication Code

HMAC-Based One-Time Password : A one-time password (OTP) algorithm based on hash-based message authentication codes (HMAC). HOTP is a cornerstone of the Initiative for Open Authentication (OATH). It was published in 2005 as an informational IETF RFC 4226. †

HOC : → Higher-order component

Hoisting : A general way of thinking about how execution contexts (specifically the creation and execution phases) work in JavaScript. While conceptually, a strict definition of hoisting suggests that variable and function declarations are physically moved to the top of the code, the variable and function declarations are instead put into memory during the compile phase. Only declarations are hoisted, not initializations. ‡

HOL blocking : → Head-of-line blocking

Holey : A property of an array that misses elements, and cannot be optimized as effectively anymore.

Home page : The initial or main web page of a website or browser. The initial page of a website is sometimes called main page as well. †

Home Page Reader : A discontinued self-voicing web browser designed for people who are blind. It was developed by IBM until 2006. †

Home screen : The main screen on a mobile operating system or computer program. Home screens are not identical because users can rearrange icons as they please, and home screens often differ across operating systems. Almost every smartphone has some form of home screen, which typically displays links to applications, settings, and notifications. †

Homepage : → Website

HomeSite : A discontinued HTML editor originally developed in 1996 by Nick Bradbury. Unlike WYSIWYG HTML editors such as FrontPage and Dreamweaver, HomeSite was designed for direct editing, or “hand-coding,” of HTML and other website languages. After a successful partnership with the company to distribute it alongside its own competing Dreamweaver software, HomeSite was acquired by Macromedia in 2001, after which elements of the software were integrated into Dreamweaver. Following the acquisition of Macromedia by Adobe, the company announced in 2009 that HomeSite would be discontinued. †

Homogenous migration : A migration where source and target systems are of the same type.

Hooking : A range of techniques used to alter or augment the behavior of an operating system, of applications, or of other software components by intercepting function calls or messages or events passed between software components. Code that handles such intercepted function calls, events, or messages is called a hook. Hooking is used for many purposes, including debugging and extending functionality. †

Hop limit : → Time to Live

Horizontal scaling : An increase in a number of resources, e.g., by adding more hard drives or servers.

Host : A computer or other device connected to a computer network. A host may work as a server offering information resources, services, and applications to users or other hosts on the network. Hosts are assigned at least one network address. Network hosts that participate in applications that use the client-server model of computing are classified as server or client systems. Network hosts may also function as nodes in peer-to-peer applications, in which all nodes share and consume resources in an equipotent manner. †

Host Identity Protocol : A host identification technology for use on Internet Protocol (IP) networks, such as the Internet. The Internet has two main name spaces, IP addresses and the Domain Name System. HIP separates the end-point identifier and locator roles of IP addresses. It introduces a Host Identity (HI) name space, based on a public key security infrastructure. The Host Identity Protocol provides secure methods for IP multihoming and mobile computing. †

Hostname : A label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication, such as the World Wide Web. Hostnames may be simple names consisting of a single word or phrase, or they may be structured. Internet hostnames may have appended the name of a Domain Name System (DNS) domain, separated from the host-specific label by a period (“dot”). In the latter form, a hostname is also called a domain name. If the domain name is completely specified, including a top-level domain of the Internet, then the hostname is said to be a fully qualified domain name (FQDN). †

Hot data : Frequently accessed data.

Hot linking : → Inline linking

HOTP : → HMAC-Based One-Time Password

Hotwire : → HTML over the wire

Houdini : A set of low-level APIs that give developers the power to extend CSS, providing the ability to hook into the styling and layout process of a browser’s rendering engine. Houdini gives developers access to the CSS Object Model (CSSOM), enabling developers to write code the browser can parse as CSS. The benefit of Houdini is that developers can create CSS features without waiting for web standards specifications to define them and without waiting for every browser to fully implement the features. ‡ ℹ︎ ishoudinireadyyet.com

HPR : → Home Page Reader

HSL : → Hue, Saturation, Lightness

HSM : → Hardware security module

HSTS : → HTTP Strict Transport Security

HSV : → Hue, Saturation, Value

HTML : → HyperText Markup Language

HTML 5 : → HTML

HTML Abstraction Markup Language : A templating system that is designed to avoid writing inline code in a web document and make the HTML cleaner. Haml gives the flexibility to have some dynamic content in HTML. Similar to other web languages like PHP, ASP, JSP, and template systems like eRuby, Haml also embeds some code that gets executed during runtime and generates HTML code in order to provide some dynamic content. † ℹ︎ haml.info

HTML over the wire : A term marking the use of HTML instead of JSON to populate web applications, and an umbrella term for Turbo, Stimulus, and Strada, tooling to help use HTML over the wire. Hotwire was presented in 2020 by Basecamp. ℹ︎ hotwired.dev

HTML template : For web components, a way to insert chunks of HTML that are then populated. HTML templates are written using the template and slot elements.

HTML-in-JS : The writing of HTML code in JavaScript, notably by using the innerHTML property.

HTML/CSS framework : A library allowing for easier web design and development using HTML and CSS. Most HTML/CSS frameworks contain at least a grid. More functional frameworks also come with more features and additional JavaScript-based functions, but are mostly design-oriented and focused around interactive UI patterns. This detail differentiates HTML/CSS frameworks from JavaScript frameworks. †

HTML5 : → HTML

HTML5 Boilerplate : An HTML, CSS, and JavaScript frontend template for creating HTML websites with cross-browser capability. † ℹ︎ html5boilerplate.com

HTTP : → Hypertext Transfer Protocol

HTTP flood attack : A type of distributed denial of service (DDoS) attack in which the attacker makes unwanted GET or POST requests in order to attack a web server or application. These attacks often use interconnected computers that have been taken over with the aid of malware. Instead of using malformed packets, spoofing, or reflection techniques, HTTP floods require less bandwidth to attack the targeted sites or servers. †

HTTP method : An HTTP action to be performed for a given resource. Although they can also be nouns, request methods are sometimes referred to as “HTTP verbs.” Each of them implements a different semantic, but some common features are shared by a group of them: e.g., a request method can be safe, idempotent, or cacheable. The methods are GET, HEAD, POST, PUT, DELETE, CONNECT, OPTIONS, TRACE, and PATCH. ‡

HTTP request method : → HTTP method

HTTP status code : An HTTP status code is issued by a server in response to a client’s request to the server. The first digit of a status code specifies one of five standard classes of responses. The classes are Informational 1xx, Successful 2xx, Redirection 3xx, Client Error 4xx, and Server Error 5xx. “200 OK,” “301 Moved Permanently,” and “404 Not Found” may be among the most common and known status codes. † : → 0–9 for various HTTP status codes

HTTP Strict Transport Security : A web security policy mechanism that helps to protect websites against protocol downgrade attacks and cookie hijacking. It allows web servers to declare that web browsers (or other complying user agents) should interact with it using only HTTPS connections, which provide Transport Layer Security (TLS/SSL), unlike the insecure HTTP protocol used alone. The HSTS policy is communicated by the server to the user agent via an HTTPS response header field named Strict-Transport-Security. HSTS policy specifies a period of time during which the user agent should only access the server in a secure fashion. †

HTTP verb : → HTTP method

HTTP/2 : A major revision of the HTTP network protocol. A major goal of HTTP/2 was to decrease latency so as to improve page load speed in web browsers. It derived from the earlier experimental SPDY protocol, originally developed by Google. HTTP/2 was developed by the HTTP Working Group (also called “httpbis,” where “bis” means “second”) of the Internet Engineering Task Force. HTTP/2 is the first new version of HTTP since HTTP 1.1, which was standardized in 1997 by RFC 2068. The HTTP/2 specification was published as in 2015 as RFC 7540. †

HTTP/3 : The upcoming third major version of the Hypertext Transfer Protocol, succeeding HTTP/2. HTTP/3 is based on a prior RFC draft, Hypertext Transfer Protocol (HTTP) over QUIC. †

httpd.conf : The main configuration file for the Apache HTTP Server. ℹ︎ is.gd/asNHfP

HTTPS : → Hypertext Transfer Protocol Secure

HTTPS Everywhere : A browser extension for Chrome, Firefox, Opera, Brave, and Firefox for Android, which is developed collaboratively by the Tor Project and the Electronic Frontier Foundation (EFF). HTTPS Everywhere automatically makes websites use a more secure HTTPS connection instead of HTTP, if they support it. HTTPS Everywhere was first released in 2010. † ℹ︎ eff.org/https-everywhere

HubDB : A relational database represented through rows, columns, and cells in a table, comparable to a spreadsheet. ℹ︎ is.gd/49zeTJ

HubL : → HubSpot Markup Language

HubSpot Markup Language : A HubSpot-proprietary extension of Jinjava which features markup unique to the HubSpot marketing and sales software.

Hue, Saturation, Lightness : An alternative representation of the RGB color model. †

Hue, Saturation, Value : An alternative representation of the RGB color model. †

Hugo : A static site generator written in Go. Hugo was released in 2013 by Steve Francia. ℹ︎ gohugo.io

Human-Computer Interaction : The study of the design and use of computer technology, focused on the interfaces between people (users) and computers. Researchers in the field of HCI observe the ways in which humans interact with computers and design technologies that let humans interact with computers in novel ways. As a field of research, human-computer interaction is situated at the intersection of computer science, behavioral sciences, design, media studies, and several other fields of study. †

humans.txt : An initiative acknowledging the people behind a website, promoting a “humans.txt” text file that features more information on the respective contributors. ℹ︎ humanstxt.org

Hungarian notation : An identifier naming convention in computer programming, in which the name of a variable or function indicates its intention or kind, and in some dialects its type (like “bBusy”, “cApples”, or “rgStudents”). The original Hungarian notation uses intention or kind in its naming convention and is sometimes called “Apps Hungarian” as it became popular in the Microsoft Apps division in the development of Word, Excel, and other apps. †

Hydration : Client-side DOM extension and manipulation of server-rendered static HTML.

Hype cycle : A branded graphical presentation developed and used by the research, advisory, and information technology firm Gartner to represent the maturity, adoption, and social application of specific technologies. The hype cycle claims to provide a graphical and conceptual presentation of the maturity of emerging technologies through five phases (Technology Trigger, Peak of Inflated Expectations, Trough of Disillusionment, Slope of Enlightenment, and Plateau of Productivity). †

Hyperlink : → Link

Hyperlink-Induced Topic Search : A link analysis algorithm that rates web pages, developed in 1999 by Jon Kleinberg. The idea behind Hubs and Authorities, as HITS is also known, stemmed from a particular insight into the creation of web pages when the Internet was originally forming; that is, certain web pages, known as hubs, served as large directories that were not authoritative in the information that they held, but were used as compilations of a broad catalog of information that led users to other authoritative pages. In other words, a good hub represents a page that pointed to many other pages, while a good authority represents a page that is linked by many different hubs. †

Hypertext : Text displayed on a computer display or other electronic devices with references (hyperlinks) to other text that the reader can immediately access. Hypertext documents are interconnected by hyperlinks, which are typically activated by a mouse click, keypress set, or by touching the screen. Apart from text, the term “hypertext” is also sometimes used to describe tables, images, and other presentational content formats with integrated hyperlinks. Hypertext is one of the key underlying concepts of the World Wide Web. †

HyperText Markup Language : The standard markup language for documents designed to be displayed in a web browser. HTML can be used together with formatting languages such as Cascading Style Sheets (CSS) and scripting languages such as JavaScript. Web browsers receive HTML documents from a web server or from local storage and render the documents into multimedia web pages. HTML and its elements describe the structure of a web page semantically, and HTML originally included cues for the appearance of the document. HTML was first presented in 1991. † ℹ︎ html.spec.whatwg.org

Hypertext Preprocessor : A general-purpose programming language originally designed for web development. PHP was created in 1994 by Rasmus Lerdorf; the PHP reference implementation is now produced by The PHP Group. PHP originally stood for “Personal Home Page,” but it now stands for the recursive initialism “Hypertext Preprocessor.” PHP code may be executed with a command-line interface (CLI), embedded into HTML code, or used in combination with various web template systems, web content management systems, and web frameworks. PHP code is usually processed by a PHP interpreter implemented as a module in a web server or as a Common Gateway Interface (CGI) executable. The web server outputs the results of the interpreted and executed PHP code, which may be any type of data, such as generated HTML code or binary image data. † ℹ︎ php.net

Hypertext Transfer Protocol : An application protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, where hypertext documents include hyperlinks and references to other resources. Development of HTTP was initiated in 1989 by Tim Berners-Lee at CERN, while the development of early HTTP Requests for Comments (RFCs) was a coordinated effort by the Internet Engineering Task Force (IETF) and the World Wide Web Consortium (W3C), with work later moving to the IETF. †

Hypertext Transfer Protocol Secure : An extension of the Hypertext Transfer Protocol (HTTP). HTTPS is used for secure communication over a computer network and widely employed on the Internet. In HTTPS, the communication protocol is encrypted using Transport Layer Security (TLS) or, formerly, its predecessor, Secure Sockets Layer (SSL). The protocol is therefore also often referred to as HTTP over TLS, or HTTP over SSL. The principal motivations for HTTPS are authentication of the accessed website, protection of privacy, and integrity of the exchanged data while in transit. The bidirectional encryption of communications between a client and server protects against eavesdropping and tampering of the communication. The authentication aspect of HTTPS requires a trusted third party to sign server-side digital certificates, which historically was expensive. †

Hypervisor : Computer software, firmware, or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is called a host machine, and each virtual machine is called a guest machine. The hypervisor presents the guest operating systems with a virtual operating platform and manages the execution of the guest operating systems. †

Hypothesis-Driven Development : A product development approach based on continuously running experiments to test hypotheses about a product, its users, and the market.

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