This article is from the Credit cards and Consumer Credit FAQ, by firstname.lastname@example.org (Steve Adams) with numerous contributions by others.
An affinity card carries the logo of an organization in addition to
the emblem of the card. It is typically a Visa or MasterCard.
Sometimes card users get frequent-flyer miles or points toward
merchandise from a catalog. The organization solicits all its
members to get cards (or even turns over its mailing list). In
return it gets some fraction of the annual fee or of the finance
charge, or some amount per transaction, or a combination of
incentives. Seldom does the organization get much money out of it:
most of the profits go to the card issuer.
See section 2, "Good deals, bad deals," for how to evaluate these