Parts are the components of your car. Depending on the specific
part, it may or may not be something your car absolutely must have
in order to function. Door panels are parts, headlight assemblies
are parts, mufflers are parts, radiators are parts, etc.
Accessories are either OEM optional equipment or aftermarket items
installed on a vehicle, and not necessarily vital to the
functioning of the vehicle. Your stereo system, car alarms, brush
guards, and 'creature comfort' items would be considered
accessories.