The MIME type text/html is used to denote the presence of an HTML source code file. This MIME type falls under the category "text".

HTML files carry the extensions HTM or HTML. HTML is the abbreviated form of Hyper Text Markup Language. It is the de facto markup language used to build web pages. It is used to denote the semantics of the structure of the text present in the web page such as paragraphs, line breaks, list features and also links and quotes. It also allows for embedding images and various programming scripts in order to provide a more feature rich web page viewing experience.

HTML is written with elements called "tags". These are expressions enclosed within angular brackets (). The HTML can be made dynamic by the use of scripting languages like JavaScript. The presentation of the HTML is further enhanced by the use of CSS or Cascading style sheets.

HTML started off as HTML 2.0 in 1995. It was named 2.0 to distinguish it from the earlier internal drafts. The current versions in use are HTML 4.01 and the ISO/IEC 15445:2000 standard version. HTML 5 is in draft at the time of writing.