Auto is short for Automobile, automotive ,automatic and is described in wikipedia
as :
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting
passengers, which also carries its own engine or motor. Most definitions of the term
specify that automobiles are designed to run primarily on roads, to have seating
for one to eight people, to typically have four wheels, and to be constructed principally
for the transport of people rather than goods.[3]
The term motorcar has also been used in the context of electrified rail systems to
denote a car which functions as a small locomotive but also provides space for passengers
and baggage. These locomotive cars were often used on suburban routes by both interurban
and intercity railroad systems.