The primary use of HTML (Hypertext Markup Language) in web development is to structure and format content on the web. HTML provides the fundamental building blocks for creating web pages, allowing developers to define elements such as headings, paragraphs, links, images, and lists. It establishes the content's layout and helps browsers render the page correctly. As a markup language, HTML is essential for creating user-friendly interfaces, enabling search engine indexing, and enhancing accessibility through semantic elements. Mastering HTML is a prerequisite for deeper understanding of other web technologies such as CSS and JavaScript.