door ajar; half-closed door; improperly closed door
Almost always refers to a car door that is not completely shut. Often used in warning contexts or when describing a door that looks closed but is not latched.
The door-ajar warning light is on.
後ろのドアが半ドアになっているよ。
The back door is not fully closed.
Compound of 半 (half) and ドア (door), literally 'half door'. The term is used for a door that is only partially closed, especially in automotive contexts.