Definition of "Door" :

noun: a swinging or sliding barrier that will close the entrance to a room or building or vehicle

"He knocked on the door."

noun: a room that is entered via a door

"His office is the third door down the hall on the left."

noun: a structure where people live or work (usually ordered along a street or road)

"The office next door."

noun: the entrance (the space in a wall) through which you enter or leave a room or building; the space that a door can close

"He stuck his head in the doorway."

noun: anything providing a means of access (or escape)

"We closed the door to Haitian immigrants."