The definition of headroom is the space between your head and something over your head such as a doorway or the top of a vehicle, or the space between a vehicle and bridges or other structures that may be over that vehicle.
The space you have been your head and the car's roof is an example of headroom.
Headroom Sentence Examples
The interior is extremely spacious and offers plenty of leg and headroom for all passengers, while the boot is positively cavernous.
All cabins are air-conditioned and have spacious twin bunks with the exception of slightly restricted headroom.
Then again it has largely negated these advances by reducing headroom.