Hyper Text Mark-Up Language (HTML) is the coding language used for creating World Wide Web pages. It is used to structure information — denoting certain text as headings, paragraphs, lists and so on — and can be used to define the semantics of a document. It allows text to be linked to another file on the Internet. HTML files are viewed with a World Wide Web browser.

Visit the following sites to learn more about HTML.

W3Schools : http://www.w3schools.com/html/default.asp
HTML Goodies : http://www.htmlgoodies.com/primers/html/
HTML Code Tutorial : http://www.htmlcodetutorial.com/
W3.org : http://www.w3.org/MarkUp/Guide/