HTML5 is the latest version of the HyperText Markup Language, the standard for creating and structuring content on the web. It introduces new elements and features that enhance the functionality, accessibility, and interactivity of websites. Key features of HTML5 include native support for audio, video, and graphics (via the <audio>, <video>, and <canvas> elements), improved support for web applications (such as local storage and offline capabilities), and semantic elements (like <article>, <section>, and <nav>) for better document structure. HTML5 also focuses on better performance, mobile responsiveness, and cross-browser compatibility, making it a key tool for modern web development.