In SEO A three-way linking is referred to as a kind of reciprocal link exchange among three-domain instead of two. Whereas, in a normal reciprocal link exchange, you and your link partner exchange link with each other. Search engines can easily identify that out a two-way link. But, in a three-way link exchange, three different domains must be involved. Say, for instance, site A link to site B, but not B to A. Now, you can see that site B is only receiving a one-way link for site A and not linking back to it. Similarly, C and A are also linked from one site but not linking back.