Editorial
Force majeure
Definition
A contractual clause excusing a party from performance on the occurrence of events beyond their reasonable control. In civil law systems it may also operate as a general principle; in common law systems it exists only if the contract provides for it.
In plain English: A clause saying nobody is in breach if something neither side could control makes performance impossible.
A civil law definition. The term may mean something different, or nothing at all, in another legal system.
Usage
English law has no general doctrine of force majeure. Without an express clause, a party must rely on frustration, which is far narrower.