Here is a detailed definition of Affiliate Marketing

Affiliate Marketing simply put is using one website to drive traffic to another and is a form of online marketing.  Although it is frequently overlooked by advertisers it can be very beneficial for both parties. While search engines, e-mail, and website syndication capture most of the attention of online retailers, affiliate marketing carries a lower profile. In spite of this, affiliates continue to play a significant role in e-retailers' marketing line of attack.

Affiliate marketing is a marketing process in which a business rewards other businesses for each visitor or customer brought about by the affiliates marketing efforts. For example if a business has a webpage and decides they would like to advertise for another business by adding a small banner or even an entire page linking to another businesses web page, they will be paid either by the amount of new leads and referrals or customers sent to that site. 

This industry has four key players:

• The merchant, retailer or brand, who advertises on affiliates web pages
• The Affiliate Network, industry “middlemen” who seek out good fits between affiliates and publishers
• The publisher or affiliate who is sending the new lead or sale
• The customer, the person surfing the web who clicks and or purchases

Affiliate marketing intersects with other Internet marketing techniques to a degree; in view of the fact affiliates often use other advertising methods.  Methods including search engine optimization, paid search engine marketing, e-mail marketing, and in some cases display advertising.  Conversely, affiliates sometimes use less accepted techniques, such as publishing reviews of products or services offered by its partners.