What is Breach Of Contract?

Legal Definition
Breach of contract is a legal cause of action in which a binding agreement or bargained-for exchange is not honored by one or more of the parties to the contract by non-performance or interference with the other party's performance. If the party does not fulfill his contractual promise, or has given information to the other party that he will not perform his duty as mentioned in the contract or if by his action and conduct he seems to be unable to perform the contract, he is said to breach the contract.

Breach of contract is a type of civil wrong.
-- Wikipedia
Legal Definition
The violation of a contractual obligation. One may breach a contract by repudiating a promise, failing to perform a promise, or interfering with another party's performance.
Legal Definition
Failure to live up to the terms of a contract. The failure may provoke a lawsuit, in which an aggrieved party asks a court to award financial compensation for the loss brought about by the breach. A legal cause of action in which a binding agreement or bargained-for exchange is not honored by one or more of the parties to the contract by non-performance or interference with the other party's performance. If the party does not fulfill his contractual promise, or has given information to the other party that he will not perform his duty as mentioned in the contract or if by his action and conduct he seems to be unable to perform the contract, he is said to breach the contract.
Legal Definition
The failure to perform a contractual obligation.
-- Ballentine's Law Dictionary