"Optional" means that something is not required or necessary, but it is available as a choice or an alternative. It is up to the individual to decide whether to use or do something that is optional.Full definition
As you might expect, it has loaded all trim levels and vehicles with optional packages with a full range of safety features. (acuraofpeoria.com)
The automakers provided information about the presence of optional features on specific vehicles by vehicle identification number (VIN). (iihs.org)
The list of optional extras includes such luxury features as the convenience key, four - zone automatic air conditioning, a dark glass panoramic roof and a cool box. (topspeed.com)