HTML, or Hypertext Markup Language, is the foundational structure used to create websites, akin to building a house with bricks and mortar. It utilizes various tags like <h1>, <p>, and <a> to define content and layout, making it essential for web developers and designers. Originally developed by Tim Berners-Lee in the early 1990s, HTML has evolved through multiple versions, with the latest, HTML5, incorporating features like multimedia support and enhanced structural elements.