What is affinity selling?

Affinity selling is a merchandising tactic used to recommend products based on the customers purchase history, as it compares to others who share similar traits with the customer in question. One can think of it is a synergy between collaborative filtering and personalization. Where collaborative filtering uses statistics to drive recommendations such as "people who bought X also bought Y" by tracking which X's are most often sold with which Y's, affinity selling takes into account the Demographics of the people making the purchases of X's and Y's such that their pairing is weighted proportionally to similarity of the person for whom the recommendation is being made.