According to IAB affiliate marketing is:
An agreement between two sites in which one site (the affiliate) agrees to feature content or an ad designed to drive traffic to another site. In return, the affiliate receives a percentage of sales or some other form of compensation generated by that traffic.
Affiliate marketing, known also as Performance marketing is a type of performance-based marketing in which a business rewards one or more affiliates for each visitor or customer brought by the affiliate’s own marketing efforts. The industry has four core players: the merchant (also known as ‘retailer’ or ‘brand’), the network (that contains offers for the affiliate to choose from and also takes care of the payments), the publisher (also known as ‘the affiliate’), and the customer. The market has grown in complexity, resulting in the emergence of a secondary tier of players, including affiliate management agencies, super-affiliates and specialized third party vendors.
Affiliate marketing overlaps with other Internet marketing methods to some degree, because affiliates often use regular advertising methods. Those methods include organic search engine optimization (SEO), paid search engine marketing (PPC – Pay Per Click), e-mail marketing, content marketing and in some sense display advertising. On the other hand, affiliates sometimes use less orthodox techniques, such as publishing reviews of products or services offered by a partner.
Affiliate marketing is commonly confused with referral marketing, as both forms of marketing use third parties to drive sales to the retailer. However, both are distinct forms of marketing and the main difference between them is that affiliate marketing relies purely on financial motivations to drive sales while referral marketing relies on trust and personal relationships to drive sales.