HTML stands for Hypertext Markup Language. It is not a programming language but rather a formatting language used to structure and present content on the web. HTML uses tags to mark up text and other content. Common tags include <html> to define an HTML document, <head> for metadata, <title> for the document title, <body> for the main content, and tags like <h1> - <h6> for headings, <p> for paragraphs, and <b>, <i>, and <u> for bold, italics, and underlined text.