(1) Also called "reciprocal linking," it is an agreement between websites to provide hyperlinks to each other in order to increase visitors and search engine page ranking. Three-way linking links site A to B, B to C and C to A, creating a less obvious relationship than between two sites and considered better for search engine optimization (SEO). See
link campaign.
(2) An organization that places advertisements from one website onto the pages of another. It ensures that the ads are divided equitably so that if site A displays an ad from site B, site B will be sure to show an ad from site A.