This is the 2984th most frequent Japanese word.
ドア
Door.
Here, "ドア" (door) is used to refer to a physical door in its general state of being open.
ドアが開いている。
The door is open.
In this sentence, "ドア" signifies the direct object in a request or command regarding the door's action.
ドアを閉めてください。
Please close the door.
Here, "ドア" is referenced as the physical object upon which an action (knocking) is performed.