Hypertext Markup Language (HTML) is a markup language that is used to structure and present content on the World Wide Web. It was created by Tim Berners-Lee in 1980. The document defines various HTML tags such as headings, paragraphs, bold, italics, lists, images, and links. It provides examples of how to use each tag, including the opening and closing syntax. Common tags discussed include <h1> for main headings, <p> for paragraphs, <b> for bold text, <i> for italics, <ol> for ordered lists, <ul> for unordered lists, and <a> for creating links between pages.