What is it called when there is a failure or refusal to perform contractual obligations?

The correct term for the failure or refusal to perform contractual obligations is "breach of contract." This occurs when one party to a contract fails to fulfill their agreed-upon duties as specified in the contract. The breach can be a complete failure to perform or a failure to meet the conditions or terms laid out in the agreement. This action often gives rise to legal remedies for the party that has been wronged, allowing them to seek damages or specific performance of the contract.

In contrast, the other terms refer to different concepts within contract law. Contract termination relates to the ending of a contract, which can happen due to various reasons, including mutual agreement or fulfillment of the contract terms. Default typically pertains to failure to meet a particular obligation, usually in the context of loans or debts, but is not specifically a term used for general contract breaches. Amendment involves making changes to the existing terms of a contract, which indicates that the contract is still valid and enforceable.