What do you mean by Quantum Meruit and state the cases where the claim for Quantum Meruit arises?

Quantum Meruit: Where one person has rendered service to another in circumstances which indicate an understanding between them that it is to be paid for although no particular remuneration has been fixed, the law will infer a promise to pay. Quantum Meruit i.e. as much as the party doing the service has deserved. It covers a case where the party injured by the breach had at the time of breach done part but not all of the work which he is bound to do under the contract and seeks to be compensated for the value of the work done. For the application of this doctrine, two conditions must be fulfilled: (1) It is only available if the original contract has been discharged. (2) The claim must be brought by a party not in default. The object of allowing a claim on quantum meruit is to recompensate the party or person for value of work which he has done. Damages are compensatory in nature while quantum meruit is restitutory. It is but reasonable compensation awarded on implication of a contract to remunerate. The claim for quantum meruit arises in the following cases: (a) When an agreement is discovered to be void or when a contract becomes void. (b) When something is done without any intention to do so gratuitously. (c) Where there is an express or implied contract to render services but there is no agreement as to remuneration. (d) When one party abandons or refuses to perform the contract. (e) Where a contract is divisible and the party not in default has enjoyed the benefit of part performance. (f) When an indivisible contract for a lump sum is completely performed but badly the person who has performed the contract can claim the lump sum, but the other party can make a deduction for bad work.