frustration指的是“合同落空”、“合同受挫”，是英美法术语的一种。元照英美法词典中是这样解释的“由于某种合同当事人不能预料或不能控制的事件发生，如当事人遭遇了不可抗力，实质性阻碍了合同当事人预期目标的实现，合同订立的基础不再存在，当事人得请求免除履行合同的义务。这是对当事人在特定情形下根据合同条款不能获得合理保护时的一种救济”。这种情形，在大陆法称为情势变迁，中国和东欧国家则称为不可抗力原则。以下为相关示例：

The Parties to a contract may be discharged from the necessity of further performance if the contract becomes frustrated. A contract may become frustrated where, before property and risk have passed, it becomes impossible to perform the contract legally, or the circumstances so  change that performance would be radically different from what was contemplated in the contract. The frustrating event must occur without the fault of either party. Examples of frustrating events are the outbreak of war or a supervening illegality, i.e. where performance becomes illegal by law after the contract.

合同落空，当事人可不再继续履行合同。合同无法依法履行或因情势变更，合同的履行与合同规定大相径庭，在财产与风险转移之前，合同可以落空。发生合同落空事项，当事人均不得有过错。合同落空的情况如战争爆发或合同订立后随即发生非法行为，即合同于订立后  其履行即为非法。