What is Vis Major?

Legal Definition
"Greater or superior force". Force majeure , specifically events over which no humans have control, and so cannot be held responsible. Equivalent to an "Act of God". Compare casus fortuitus (see above).
Legal Definition
A superior force. In law it signifies inevitable accident.

2. This term is used in the civil law in nearly the same same way that the words act of God, (q. v.) are used in the common law. Generally, no one is responsible for an accident which arises from the vis major; but a man may be so where he has stipulated that he would; and when he has been guilty of a fraud or deceit. 2 Kent, Com. 448; Poth. Pret a Usage, n. 48, n. 60 Story Bailm. ยง25.
-- Bouviers Law Dictionary
Legal Definition
A greater or superior force; an irresistible force. This term is much used iu the law of bailments to denote the interposition of violence or coercion proceeding from human agency, (wherein it differs from the "act of God,") but of such a character and strength as to be beyond the powers of resistance or control of those against whom it is directed; for example, the attack of the public quemy or a band of pirates. See The George Shiras, 61 Fed. 300, 9 C. C. A. 511; Brousseau v. The Hudson, 11 La. Ann. 428: Nugent v. Smith, 1 C. P. Div. 437. In the civil law, this term is sometimes used as synonymous with "vis divina," or the act of God. Calvin.
-- Black's Law Dictionary
Legal Definition
Act of God; an event which, as between the parties and for the purpose of the matter in hand, cannot be definitely seen or controlled. See 162 Ind. 278, 102 Am. St. Rep. 203, 1 Ann. Cas. 460, 65 L. R. A. Ill, 70 N. E. 264.
-- Ballentine's Law Dictionary