HTML (Hypertext Markup Language) is a system of markup symbols used to create web pages, where tags dictate the display of text and images in browsers. The document outlines the basic structure of HTML, including elements such as <html>, <head>, <title>, and <body>, as well as formatting tags like <b> for bold text and <i> for italics. It also explains the use of text editors to write HTML, emphasizing the importance of correct tag usage to achieve the desired visual presentation.