refers to links between websites whose owners have agreed to provide a link to each other's sites. Has gained popularity due to ratings by search engines and directories, however, over-linking can lead to being banned from search engines.
This is when you exchange links with another website. That is, they add a link from their site to yours and you add a link from your site to theirs.
links exchanged between two sites, generally on an agreement by the site owners to exchange links.