Definition
HTML (HyperText Markup Language) is use to identify web documents (web pages).
Hypertext allows document text to be “linked” to another file on the internet.
A markup language allows for the processing, definition, and presentation of text; the code used to specify the formatting are called tags.
In HTML, a block of text is surrounded by codes called HTML tags that describe the document content and how it should appear.[1][2]
See w3schools.com for more information.

From http://www.w3schools.com/html/html_intro.asp
References
- ^ American Marketing Association, AMA Dictionary.
- ^ w3schools.com, HTML Introduction.