Definitions beginning with H

H1

First-level HTML heading, generally used for the page’s main topic. Subsequent levels organise content; choose them by structure rather than desired visual size.

Source consulted : W3C · 2026-10-17

In practice: use the main heading to name the real page topic without artificial repetition.

Hallucination

Confidently produced answer containing invented, distorted or insufficiently supported information.

In practice: check names, figures, quotations and links against their sources before sharing.

Hamburger menu

Navigation button represented by horizontal lines and used to open a compact menu, especially on mobile.

In practice: Check that important sections remain discoverable and the button announces whether it is open or closed.

Hard requirement

Essential condition set before a comparison; an option that fails it leaves the shortlist even if it performs well on other criteria.

In practice: separate three essential conditions from preferences before evaluating options.

Hashing

Computation of a fixed-size digest from data. Cryptographic hashing aims to make inversion and collisions impractical; it is not reversible encryption.

Reference: NIST CSRC · Hash function · Source consulted 2026-10-31

Source consulted : MDN · Hash function · 2026-10-31

Hashtag

Word or phrase preceded by # used to group or discover posts on some platforms.

In practice: Choose a clear word and check its context before adding it to a post.

Head

HTML element collecting document metadata, including its title, encoding and resource references. It differs from header, used for visible introductory content. A title declared in head should remain consistent with the page’s subject and main content.

Reference: MDN : HTML head element · Source consulted 2026-10-18

In practice: Check titles, metadata and resource loading on every page template.

Headless CMS

CMS managing content without imposing a display interface and generally distributing it through an API.

In practice: assess content editing, the API and the public interface separately; this separation adds technical responsibilities.

Heatmap

Heatmap visualizing areas of attention, clicks or scrolling from usage data.

In practice: Use the map to form a hypothesis, then observe consented or tested individual journeys.

Hero section

Prominent visual area at the top of a page generally presenting the main message and primary action.

In practice: show the page’s subject, value and relevant next step immediately.

HMAC

Authentication code calculated using a hash function and shared key. It helps verify message integrity and origin; it does not encrypt the message contents.

Reference: GitHub : Validating webhook deliveries

Source consulted : MDN · 2026-10-17

Use a valid synthetic event, then alter its content: validation should reject the second before business processing.

hreflang

Annotation linking equivalent language or regional page versions to help search engines serve the appropriate variant. Connect equivalent content pages and check return links, including self-reference. A language variant should not point to an unrelated page.

Reference: Google Search Central · Localized versions · Source consulted 2026-10-25

In practice: Check that each variant points to the others and that listed URLs are canonical and reachable.

HSTS

Instruction received over HTTPS directing a browser to use HTTPS for a domain for a defined period. It may cover subdomains. Before extending coverage, check their actual support; an HTTPS redirect and an HSTS policy do not perform exactly the same role.

Reference: MDN : Strict-Transport-Security · Source consulted 2026-10-18

In practice: confirm HTTPS works on all affected subdomains before broad deployment.

HTML

Markup language giving content structure and meaning through headings, paragraphs, links, lists and form fields. Elements have roles and sometimes native behaviours. CSS primarily handles presentation, while JavaScript can add interactions.

Reference: MDN : HTML · Source consulted 2026-10-18

In practice: choose elements by purpose, then test headings, links and controls by keyboard.

HTTP

Protocol for exchanging messages between clients and servers through requests and responses. HTTP defines methods, headers and statuses; HTTPS protects transport using TLS. The same URL can produce different responses depending on method, headers or permissions. Inspect the complete exchange before concluding that a service failed.

Reference: IETF · RFC 9110, HTTP Semantics · Source consulted 2026-10-25

Source consulted : MDN · 2026-10-17

In practice: inspect method, status and headers of a request before diagnosing a page.

HTTP 103 Early Hints

An interim HTTP response that can announce resources before the final response, allowing earlier connections or loading. It does not replace the final status, and benefits depend on resources and browser.

Reference: MDN : 103 Early Hints · Source consulted 2026-10-18

In practice: Measure real loading and check that hinted resources are actually used.

HTTP 410 status

HTTP response indicating that a resource is no longer available and its absence is considered likely permanent. It suits an intentional removal; temporary unavailability needs a different diagnosis.

Source consulted : MDN · 2026-10-17

In practice: check the status code actually returned by the server.

HTTP header

Field accompanying an HTTP request or response to specify information such as content type, caching or authentication. It is distinct from the body carrying the page or data. Check values actually received because an intermediary can affect the exchange.

Reference: MDN : HTTP headers · Source consulted 2026-10-18

In practice: inspect headers on the final response, including after redirects and caching.

HTTP status code

Numeric HTTP response code describing request handling. Read it with the method and context; a visually correct page can return an incorrect status. Distinguish the returned status from displayed content: a “not found” message accompanied by 200 still announces success at protocol level.

Reference: IETF · RFC 9110, HTTP Semantics · Source consulted 2026-10-25

Source consulted : MDN · 2026-10-17

In practice: check the final status and redirect chain, not just displayed content.

HTTP-01 challenge

ACME validation of control over a name through an HTTP resource expected by the certificate authority.

Reference: Let’s Encrypt : Challenge Types

Verify that routing exposes the validation resource in the test environment.

HTTP/2

HTTP version changing how exchanges are framed and transported, including multiple streams on a connection. Methods and statuses retain their meanings. Enabling it does not fix a slow server, unnecessary files or expensive scripts; measure the journey under relevant conditions.

Reference: MDN : HTTP/2 · Source consulted 2026-10-18

In practice: verify negotiation and real measurements before crediting the protocol with a gain.

HTTP/3

HTTP version using QUIC over UDP instead of the TCP transport used by earlier versions. It changes transport handling while retaining HTTP concepts. Effects depend on the network and endpoints; the version number is not a speed guarantee.

Reference: MDN : HTTP/3 · Source consulted 2026-10-18

In practice: check compatibility, fallback and response times on representative networks.

HTTPS

HTTP protected by TLS to encrypt exchanges and verify server identity through its certificate. This protects transport. It establishes neither editorial reliability nor absence of malicious software or correct authorisation of the site’s operations.

Reference: MDN : HTTPS · Source consulted 2026-10-18

In practice: check certificate validity and mixed content on public pages.