What is affiliate marketing:  a marketing or advertising arrangement that an online product or service owner pays a commission to a third party (affiliate) when that affiliate sells their product or service via the affiliate’s website or email marketing.

or same definition in different words from google.

Affiliate marketing is when a product owner allows other marketers to sell his product and receive a percentage of the sale. … This is different from a pay per click program because an affiliate does not make any money from the product owner unless he sells something.