HTML (Hypertext Markup Language) is the standard markup language used to create web pages. HTML uses tags to define elements like paragraphs, headings, links, images, and tables. Common tags include <p> for paragraphs, <h1> - <h6> for headings, <a> for links, <img> for images, and <table> for tables. HTML pages can also include styles, lists, forms, iframes and other elements. Well-formed HTML code ensures web pages display properly across different browsers.