HTML (Hypertext Markup Language) is the fundamental building block of web pages. It provides the structure and content of a website by using tags to define various elements and their attributes. HTML allows web browsers to interpret and display text, images, links, videos, and interactive features. It uses a hierarchical structure, with elements nested inside one another to create a logical order. By employing tags such as headings, paragraphs, lists, tables, and forms, developers can organize and present information effectively. HTML also supports the inclusion of CSS (Cascading Style Sheets) and JavaScript, enabling designers to enhance the appearance and functionality of web pages. It is a crucial language for creating accessible and visually appealing websites across different platforms and devices.