Answer

Three way linking is a way of linking 3 sites together without making the reciprocation obvious. For example, sites A,B,C and site A linking to B, B linking to C and C linking to A. Most three way linking activites are done with the intention of manipulation search results and is generally not recommended as it falls against the Google SEO guideline of "Don't participate in link schemes designed to increase your site's ranking or PageRank." While there are legitimate reasons for three way linking, most requests are parts of larger link schemes whereby the webmaster is using multiple, sites, servers and IP addresses to hide the ownership relation from Google.