What is Alternative Pleading?

Legal Definition
Alternative pleading is the legal term in the law of the United States for a form of pleading that permits a party in a court action to argue multiple possibilities that may be mutually exclusive by making use of legal fiction.

A pleading in the alternative sets forth multiple claims or defenses either hypothetically or alternatively, such that if one of the claims or defenses are held invalid or insufficient, the other claims or defenses should still have to be answered.
-- Wikipedia
Legal Definition
a suit that is given in such terms that of the several facts presented it is not sure which the attorney will base the case on.