Reciprocal link

Alternatively referred to as a link exchange, a reciprocal link is a link that is placed on a web page in exchange for the other web page to link to your web page. Part of how search engines like Google rank web pages in their search results is by how many different pages link to a page and how popular those pages are. By participating in link exchanges with other popular pages you can increase your rank in search engine results.

Also see: Internet definitions, Link, PageRank, SEO