Unknown or unspecified; used when details are not known or not provided (often in forms or descriptions).
年齢不詳の俳優が主演を務めた。
An actor of unknown age played the lead role.
出所不詳の手紙が届いた。
A letter of unknown origin arrived.
原因は不詳だが、機械が突然停止した。
The cause is unknown, but the machine stopped suddenly.