Русско-англо-русский юридический словарь

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. (Wikipedia)

In the United States, a liquidated damage clause is intended to estimate damages in the event of non-performance or breach of contract. [...] The intent of liquidated damages is simply to measure damages that are hard to prove once incurred. If the liquidated damages are disproportionate, they can, however, be declared a penalty. The clause is then void, and recovery will be limited to the actual damage that results from the breach. [...]

In civil law countries, the attitude toward contractual penalties is quite different from the common law approach. The Napoleonic Code, upon which most civil codes are based, allowed for penalties to encourage performance of contractual obligations. (This is the precise rationale that is rejected in the United States.) (lexology.com)

In the Institute’s Principles, non-performance of obligations is considered in general term and covers cases such as delay in performing the transaction, unsuitable performance of the obligation and the performance of banned actions. (Comparative Study of Damages by Non-performance of Obligations in UNIDROIT Principles, Islamic Jurisprudence and Iranian Laws)

Non-performance is failure by a party to perform any of its obligations under the contract, including defective performance or late performance. (Article 7.1.1 of UNIDROIT PRINCIPLES 2010)