The aftermarket auto warranty, also known as the extended auto warranty, is simply that warranty which provides extra or additional warranty coverage to a vehicle with an existing warranty.  It may also be used to provide warranty coverage for the vehicle without any current warranty coverage.

The aftermarket auto warranty, also likened to a service warranty, is one that must be purchased separately from the vehicle during purchasing transactions.  It may or may not be purchased simultaneously with the vehicle however, and it can be purchased from any other dealer or provider for a stipulated period after the purchase of the vehicle and still be able to provide coverage for the vehicle during the time lapse between the two purchases.
The aftermarket auto warranty may be able to extend the coverage on a vehicle whose existing warranty coverage is due to expire soon, or it may be able to extend the terms of the coverage such that a limited warranty coverage may be converted into a fully comprehensive coverage.  Likewise, it may be able to extend the mileage coverage on a vehicle.  For the vehicle without any warranty coverage, it can be selected to provide any type of coverage that the vehicle owner may desire.