Quid pro quo (Latin for "what for what") is used to mean something for something. Quid pro quo is a legal term for the transaction of valued items or favors, in return for giving something of value. For a contract to be binding, it usually must involve the exchange of something of quantifiable value, however, quid pro quo is widely used in the context of describing political favors, as given in apparent exchange for money.
For democratic public officials with special powers of government, favors given in quid pro quo constitute a breach of the public trust and a dishonest circumventing of democratic process, for special interests. In the context of political favors, quid pro quo, being secretive, may find widely varied avenues for how such transactions (believed quid pro quo) might take place. Among these are straight - favors for cash transactions, political campaign contributions, third-party campaigns and related assistance, and favors for favors (quite common in government). The last, favors for favors, refers to officials of different or equal capacities, each in league with special interests, similar or otherwise; exchanging favors, based on an estimated equality of their value.
A more informal term is "tit for tat".
See: campaign finance reform.