Definition
HyperText Markup Language (HTML) is the markup language that defines the structure and content of web pages, describing headings, paragraphs, links, images and more with elements and attributes. WHATWG maintains it as the HTML Living Standard.
How it works
The browser fetches an HTML document, parses it into a DOM tree, and combines CSS and JavaScript for rendering and interaction. Elements are written as tags (such as <a>, <p>, and <img>), and semantic elements also convey meaning to search engines and assistive technologies.
Usage
HTML underpins every web page; embedded HTML also appears in email templates and document export formats.
Related and confusable terms
The DOM is the programmable tree the browser builds after parsing HTML — not the same thing. Markdown is a simpler syntax that is usually converted to HTML, and JSON holds structured data rather than document structure.