Affiliate Marketing is an Internet-based marketing practice in which a business rewards one or more affiliates for each visitor or customer brought about by the affiliate's marketing efforts. The Affiliate Marketing industry has four core players at its heart: the Merchant, the Network, the Publisher and the Consumer. The market has grown sufficiently in complexity to warrant a secondary tier of players, including Affiliate Management Agencies, Super-Affiliates and Specialized Third Parties vendors.
source: wikipedia.org/wiki/Affiliate_marketing