A portal of entry into a building, room, or vehicle, consisting of a rigid plane movable on a hinge. Doors are frequently made of wood or metal. May have a handle to help open and close, a latch to hold the door closed and a lock that ensures the door cannot be opened without the key.

“I knocked on the vice president's door”

Any flap, etc. that opens like a door.

“the 24 doors in an Advent calendar”

(immigration) An entry point.

To cause a collision by opening the door of a vehicle in front of an oncoming cyclist or pedestrian.