'Consideration' is something that is paid or is promised to be paid to somebody in return of some favour that he has done to you. it may be money, a thing or some other favour. except few exceptions any contract without consideration is void. however, the quantity of the consideration is almost immaterial in contract.

Something of value to either the promisee or the promisor of a contract (usually cash, but also property, a promise to do something or not to do something, and so on) that is given or will be given by the promisee to the promisor in exchange for a performance or a promise of a performance by the promisor. For the contract to be enforceable, the consideration must be something that the promisee, to his or her detriment or loss, is giving up, or something that benefits the promisor.
gratuitous consideration
Consider-ation that is neither a detriment or loss to a promisee nor a benefit to the promisor. For example, the promise to pay for an item with something that is worthless to both the promisee and the promisor is gratuitous consideration. A contract based on such consideration is unenforceable.

According to Indian contract Act:
When, at the desire of the promisor, the promisee or any other person has done or abstained from doing, or does or abstains from doing, or promises to do or to abstain from doing, something, such act or abstinence or promise is called a consid­eration for the promise. [section 2(d)].

CONSIDERATION - The inducement, price or motive that causes a party to enter into an agreement or contract. Something of value that is given in exchange for getting something from another person. For example, rent payments paid to receive the right to rent an apartment. Negotiable instruments, as bills of exchange and promissory notes, carry with them prima facie evidence of consideration. The consideration must be some benefit to the party by whom the promise is made. Considerations are good when they are for natural love and affection; or valuable when some benefit arises to the party to whom they are made, or inconvenience to the party making them. In respect of time, a consideration is either: Executed, or Something done before the making of the obligor's promise. In general, an executed consideration is insufficient to support a contract but an executed consideration on request or by some previous duty, or if the debt be continuing at the time, or it is barred by some rule of law, or some provision of a statute as the act of limitation, it is sufficient to maintain an action; Executory, or something to be done after such promise; Concurrent, as in the case of mutual promises, and; A continuing consideration.

Definition of ‘consideration’ - When, at the desire of the promisor, the promisee or any other person has done or abstained from doing, or does or abstains from doing, or promises to do or to abstain from doing, something, such act or abstinence or promise is called a consid­eration for the promise. [section 2(d)].

This as per contract act 1882