day room; lounge; social hall
A common room for socializing, especially on a ship or in a hotel. The term is straightforward and not particularly rare.
I talked with other passengers in the ship's day room.
The hotel lounge closes at 10 p.m.
Compound of 社交 (socializing) and 室 (room). The exact origin is uncertain, but it likely arose as a translation of English 'social room' or 'day room' in the context of ocean liners and hotels.