Substantial performance is a term used in contract law to refer to a degree of performance of a contract which isn't full and complete performance, but is so nearly equivalent that it would be unfair to deny the contractor the payment agreed upon in the contract. However, the owner has a right to recover whatever damages he has suffered by reason of the contractor's failure to render full and complete performance.
The plaintiff must have at least substantially performed the plaintiff’s side of a bargain before the plaintiff can call on the defendant to perform the defendant’s side of the bargain e.g. by paying an agreed amount. What actually constitute substantial performance depends on the circumstances.