HyperText Markup Language (HTML) is the main markup language for web pages. HTML elements are the basic building-blocks of webpages.
HTML is written in the form of HTML elements consisting of tags enclosed in angle brackets (like
<html>), within the web page content. HTML tags most commonly come in pairs like
</h1>, although some tags, known as empty elements, are unpaired, for example
<img>. The first tag in a pair is the start tag, the second tag is the end tag (they are also called opening tagsand closing tags). In between these tags web designers can add text, tags, comments and other types of text-based content.
The purpose of a web browser is to read HTML documents and compose them into visible or audible web pages. The browser does not display the HTML tags, but uses the tags to interpret the content of the page.
Web browsers can also refer to Cascading Style Sheets (CSS) to define the appearance and layout of text and other material. The W3C, maintainer of both the HTML and the CSS standards, encourages the use of CSS over explicitly presentational HTML markup.
copy description from:: http://en.wikipedia.org/wiki/HTML