A somewhat formal term for a room used for daily living. In casual speech for a family living room, 居間 or リビング is often more natural.
The living room in this apartment faces south and is bright.
In winter, I try not to forget to ventilate the living room.
Hospitalized patients spend much of their time in their room.
A staff member entered the room to check on things.
部屋 is a general word for any room, while 居室 specifically denotes a room used for daily living.
居室 refers to a living space shared or used for daily life, while 個室 means a private, individual room (e.g. in a hospital or hotel).
monk's cell; solitary room
Sino-Japanese compound of 居, associated with residing or being present, and 室, meaning room. The spelling directly reflects the idea of a room one lives in or occupies.