Dunlop v selfridges. Definition here is the price you pay for the others promise that is, anything of value that the parties have agreed to exchange. In the absence of consideration the courts would not enforce an agreement. The case of edmons v Lawson is a good example.
It may consist of a promise to perform a desired act or a promise to refrain from doing an act that one is legally entitled to do. In a bilateral contract—an agreement by which both parties exchange mutual promises. In a unilateral contract, an agreement by which one party makes a promise in exchange for the other's performance, the performance is consideration for the promise, while the promise is consideration for the performance. Consideration must have a value that can be objectively determined. For example, a promise, to make a gift, the law does not enforce gifts unless they are made by deed or a promise of love or affection is not enforceable because of the subjective nature of the promise eg balfour v balfour .Consideration identifies the types of agreements that are to be treated as enforceable contracts. Where ever the parties need to vary the terms of the original agreement they will need to provide fresh consideration. . There are two types of consideration.
Executed, is typical in unilateral contacts where in one party has undertaken everything they were supposed to do, and the other party just has to act on it for example carill v carbolic smoke Executory, no performance takes place at the