The text displayed as the link in a text link:
<a href="link.html">Anchor Text</a>
The anchor text gives search engines clues as to what the content on the other end of the link is about. Search engines use the anchor text of a link as a form of outside verification, and as a result have become one of the most important elements in search engine rankings.
In recent years, however, it has been speculated that having keyword optimized anchor text on too many of the links pointing to your site can cause Google to penalize or even ban your site from their search results completely.