HTML (Hypertext Markup Language) is the standard markup language used to create web pages. HTML uses tags to define the structure and layout of a web page. Some key HTML elements include headings, paragraphs, links, images, and lists. Attributes provide additional information about HTML elements and are specified in start tags. Common attributes include href for links, src for images, and style for formatting. HTML documents have a specific structure with a DOCTYPE, html, head, and body tags.