Quid pro quo
（重定向自Quidproquo）
Quid pro quo ("something for something" or "this for that" in Latin) means an exchange of goods or services, where one transfer is contingent upon the other. English speakers often use the term to mean "a favour for a favour"; phrases with similar meaning include: "give and take", "tit for tat", and "you scratch my back, and I'll scratch yours".