Good question! A dome light in a car is generally considered to be any light whose purpose is to illuminate the cabin or interior of a vehicle.
Dome lights can either be automatic, manual, or both—dome lights in the front row will come on automatically when a car door is opened and serve as a reminder that a door needs to be closed.
Many dome lights also allow the driver or passengers to switch them on and off manually. This allows for easy illumination of the cabin or backseat when it is dark out, making it easier to read, find, or otherwise see the vehicle’s interior.