HTML (Hypertext Markup Language) is the code that defines the structure and layout of a web page. It uses tags, which are words surrounded by <>, to annotate text and other content for display. The basic structure of an HTML page requires <html>, <head>, and <body> tags. The <head> contains metadata like the <title>. The <body> is where visible content like text, headings, images, and paragraphs appear. Formatting tags like <b> for bold, <i> for italics, and <p> for paragraphs are used to style text. The document provides instructions on how to code a basic HTML page with headings, images, and paragraphs.