HTML
The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It defines the meaning and structure of web content.

History
HTML (HyperText Markup Language) was conceived by physicist Tim Berners-Lee in 1989 at CERN. IThe first public description appeared in 1991, specifying 18 elements. Formalization occurred with the mid-1993 "Hypertext Markup Language (HTML)" Internet Draft by Berners-Lee and Dan Connolly. HTML 2.0, the first standard specification, was finalized in 1995 by the IETF's HTML Working Group. Since 1996, maintenance transitioned to the World Wide Web Consortium (W3C), and HTML became an international standard in 2000. The most recent major iteration, HTML5, was completed in 2014, co-developed by W3C and the Web Hypertext Application Technology Working Group (WHATWG).
Markup
HTML markup consists of several key components, including those called tags (and their attributes), character-based data types, character references and entity references. HTML tags most commonly come in pairs like <h1> and </h1>, although some represent empty elements and so are unpaired, for example <img>. The first tag in such a pair is the start tag, and the second is the end tag (they are also called opening tags and closing tags).