未履行合同 meaning in English

failure of performance
failure to perform

The possessory lien referred to in the preceding paragraph means the right of the ship builder or repairer to secure the building or repairing cost of the ship by means of detaining the ship in his possession when the other party to the contract fails in the performance thereof
前款所称船舶留置权，是指造船人、修船人在合同另一方未履行合同时，可以留置所占有的船舶，以保证造船费用或者修船费用得以偿还的权利。
766 provides that : “ one who intentionally and improperly interferes with the performance of a contract ( except a contract to marry ) between another and a third person by inducing or otherwise causing the third person not to perform the contract , is subject to liability to the other for the pecuniary loss resulting from the failure of the third person to perform the contract
《美国侵权法重述，第二版》（ 1977 ）规定了“第三人故意干涉合同履行” ，其中第766规定：通过引诱而故意或者不适当地干涉他人与第三人之间的合同关系（婚姻合同除外），或者致使第三人不履行合同义务，则第三人未履行合同义务而造成的经济损失则应由干涉方承担。