In order for a contract to be binding it must be supported by valuable consideration. That is to say, one party promises to do something in return for a promise from the other party to provide a benefit of value (the consideration)
Consideration is what each party gives to the other as the agreed price for the other's promises. Usually the consideration is the payment of money but it need not be; it can be anything of value including the promise not to do something, or to refrain from exercising some right.
The payment doesn't need to be a fair payment. The courts will not intervene where one party has made a hard bargain unless fraud, duress or unconscionable conduct is involved.2