A type of affiliate marketing program where the advertiser pays the affiliate based on conversion of sales. If a customer follows an affiliate link to the advertiser's site and makes a purchase in accordance with the affiliate agreement, the affiliate is paid. Affiliates can earn a higher commission through pay-per-sale affiliate programs, however these types of programs usually have the lowest conversion rate.
See "How Affiliate Marketing Works" in the "Did You Know..." section of Webopedia.
Also see Refer-It.com, a directory of referral & affiliate programs for e-commerce, featuring information on over 6,500 affiliate programs.