Bartering
Also known as: barter deal
Bartering is a form of business in which no payment is made in money for a product or service, but a return service is provided. Bartering is thus a kind of barter deal. Bartering deals occasionally happen in the (online) marketing world. In exchange for advertising space or airtime, products are offered to the publisher of the website or other medium.
Marketing through contests/competitions is also classified under bartering.