A link trading structure in which there are no reciprocal links. Page A links to page B, and page B links to page C. Usually page A and page C are owned by the same webmaster and page C links to page A, so while links are actually being traded between to webmasters there are no actual reciprocal links. Many view this to be superior to a reciprocal link for SEO, but most smart webmasters will have a balance of both reciprocal links and ABC links.