HTML (HyperText Markup Language) is the markup language that describes the structure and content of a web page: headings, paragraphs, links, images, forms.
It is not a programming language: it contains no logic. It tells the browser what each element is, using tags (h1 for a heading, p for a paragraph, a for a link). Styling is handled by CSS, interactivity by JavaScript.
Created by Tim Berners-Lee in the early 1990s along with the web itself, HTML is now a living standard, updated continuously rather than through major versions.
Well-written HTML is called semantic: each tag matches the meaning of the content. This matters for accessibility (screen readers), for search engine optimization and for code maintainability.
Why it matters when hiring
Every web developer knows HTML, so it is not a screening criterion in itself. What sets a good front-end developer apart is semantic, accessible HTML, often neglected in favor of frameworks. If accessibility matters to you (public services, legal obligations), have it checked in the interview: the skill is less common than people think.