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.
このマンションの居室は南向きで明るい。
The living room in this apartment faces south and is bright.
Hospitalized patients spend much of their time in their room.
冬は居室の換気を忘れないようにしている。
In winter, I try not to forget to ventilate the living room.
A staff member entered the room to check on things.
居室 sounds formal or bureaucratic, whereas リビング is the casual, modern loanword used in daily conversation for a living room.
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.