HTML5 is the fifth major version of the Hypertext Markup Language — the standard markup language for creating web pages and applications. It introduced semantic elements, multimedia support, form enhancements, and powerful APIs that transformed the web from a document platform into a full application ecosystem. Modern browsers implement HTML5 as a living standard, continuously evolving through WHATWG. One critical insight: HTML5's true power lies not in replacing JavaScript frameworks but in reducing reliance on them — native features like <dialog>, <details>, and form validation eliminate thousands of lines of custom code while improving accessibility and performance.