HTML, short for Hypertext Markup Language, is a tag-based language used for creating web pages. It consists of markup symbols, known as elements or tags, which instruct web browsers on how to display information. Each element has a start and end tag, and some are self-closing. HTML includes attributes that provide additional information to elements. Named character references are used to give special meanings to characters like <, >, &, and ". HTML also supports comments for programmers to understand and collaborate on code. Additionally, HTML documents require a Doctype declaration at the beginning, specifying the version of HTML used, such as in HTML5.