The Latin phrase quid pro quo means making a certain kind of deal: you do this for me, and I'll do that for you.
Ever hear the expression, "You scratch my back, I'll scratch yours"? That describes a quid pro quo: doing a favor you expect to be paid back, instead of doing the favor for its own sake. Politicians are often accused of doing a quid pro quo: someone donated to their campaign and is now getting favors in return. Quid pro quo definitely has a shady feel, but it just means making a deal that trades one thing for another.