A widely used markup language for structuring documents on the Internet. Text and media within a document are marked by a series of ‘tags’ to denote their structural relationship with other parts of the document and other documents on the Internet. For example, Chapter One specifies that the text “Chapter One” is a first-level heading within the document. The presentation of the text can be set within the tags, for example font size, but should normally be specified by means of a collection of presentation styles to allow for greater accessibility of the document to those with disabilities. In addition there are a number of programming notations that can be embedded in, or used to generate, HTML to facilitate advanced data handling.

http://www.simplehtmlguide.com/ An interactive guide to HTML