Civil law. A contract which involves mutual and reciprocal obligations, and wherein the acts to be done and performed on one side form the consideration for those to be done and performed on the other. One in which each of the contracting parties gives and, receives an equivalent. The contract of sale is of this kind. The seller gives the thing sold, and receives the price, which is the equivalent. The buyer gives the price and receives the thing sold, which is the equivalent. These contracts are usually distributed into four classes, namely; Do ut des; Facio ut facias; Facio ut des; Do ut facias.