That which is done without authority, as a signature or indorsement made without actual, implied or apparent authority and this includes a forgery. U.C.C. No. 1-201(43)
@ unauthorized use
The criminal offense of use of a motor vehicle without authority of the owner, knowing that such use is without his permission. It differs from larceny to the extent that in the crime of unauthorized use, the government need not prove the intent to deprive permanently the owner of the vehicle.

Black's law dictionary. . 1990.