A sponsorship is the exchange of financial/non-financial benefits or other services for an advertising performance. It is very important to differentiate between a sponsorship and a donation - especially in the amateur-sports sector or the cultural field. A donator does not recieve anything in return while a sponsor will always get public recognition in the form of advertising. Even small actions like linking the sponsor on the sponsee's homepage or adding a logo to it are defined as advertising.
By agreeing to a sponsorship, a sponsoring-contract is often signed. This is especially important for the sponsor if he does not recieve a bill but still wants to allege the sponsorship as operating costs.