inside a room; interior of a room
General term for the inside of any room. Often used in descriptive or formal contexts.
There was no one inside the room.
inside a bedroom; interior of a bedchamber
Specifically refers to the interior of a bedroom or private chamber. Less common in modern everyday speech; often appears in literary or historical contexts.
He was quietly reading a book inside his bedroom.
Taoist sexual alchemy
Compound of 房 (room, chamber) and 中 (inside, middle). The reading ぼうちゅう follows standard on'yomi.