Don’t know what backlinks are? Read this first.
3 way backlinks are when you have 3 websites. Lets take sites A, B and C. So site A has a link to site B and site B has a link to site C and site C has a link to site A. Think of a triangle. Why is this important? Building backlinks are very important, but this is considered a “blackhat” way of building links. What is wrong with this technique? Google will either blacklist you or lower your page rank if they catch you doing this.
The purpose of a 3 way link is to build your own “fake” backlinks quickly. This will create higher search engine results very fast. I have personally been able to achieve #1 results on Google in minutes. Read this on manipulating Google’s algorithm.
There are services that provide 3 way links, but again… you need to know the consequences of this type of marketing. I do not recommend this type of marketing because there are relatively easy ways to build legitimate backlinks.