The term "legroom" refers to the amount of space between a passenger's seat and the one in front of it, allowing enough room for their legs. On an airplane or train, legroom is important because passengers need to be able to stretch out their legs comfortably during long trips.
The phrase "headroom" on the other hand refers to the amount of space above a passenger's seat, providing enough clearance for them to sit upright without hitting their head on the ceiling or overhead compartment. This is important because it allows passengers to be comfortable and avoid discomfort or injury while seated.