HTML is an acronym for Hypertext Markup Language and is a text-based markup language used to create documents for the web. HTML is used to create a structure for the content and CSS to define the style of the content. Additionally, HTML documents contain metadata (e.g. the page's language).
Browsers interpret HTML documents and display its content accordingly (e.g. as text or image).
HTML is developed by the W3C and the WHATWG.