noun /ˌkwɪd.pɹəʊˈkwəʊ,ˌkwɪd.pɹoʊˈkwoʊ/
a) Something understood as another ; an equivocation.
We had no money so we had to live by quid pro quo.
b) This for that; giving something to receive something else ; something equivalent ; something in return.
Wikipedia foundation.