Unauthorized use of a motor vehicle refers to the use of a motor vehicle for a person's own purpose without the consent of the owner. The vehicle is used or retained for purposes not consented or authorized by the owner. This amounts to an offense and there are state specific laws on the subject.
Example of a State Statute ( Oregon) on Unauthorized use of a motor vehicle.
In Oregon, ORS § 164.135 makes unauthorized use of a motor vehicle a Class C felony.
The relevant law as it appears in the statute.
164.135. Unauthorized use of a vehicle.
(1) A person commits the crime of unauthorized use of a vehicle when:
(a) The person takes, operates, exercises control over, rides in or otherwise uses another's vehicle, boat or aircraft without consent of the owner;
(b) Having custody of a vehicle, boat or aircraft pursuant to an agreement between the person or another and the owner thereof whereby the person or another is to perform for compensation a specific service for the owner involving the maintenance, repair or use of such vehicle, boat or aircraft, the person intentionally uses or operates it, without consent of the owner, for the person's own purpose in a manner constituting a gross deviation from the agreed purpose; or
(c) Having custody of a vehicle, boat or aircraft pursuant to an agreement with the owner thereof whereby such vehicle, boat or aircraft is to be returned to the owner at a specified time, the person knowingly retains or withholds possession thereof without consent of the owner for so lengthy a period beyond the specified time as to render such retention or possession a gross deviation from the agreement.
(2) Unauthorized use of a vehicle, boat or aircraft is a Class C felony.(3) Subsection (1)(a) of this section does not apply to a person who rides in or otherwise uses a public transit vehicle, as defined in ORS 166.116, if the vehicle is being operated by an authorized operator within the scope of the operator's employment.