a room, usually at a school or university, set aside for the common use of everyone. It usually has comfortable chairs for reading or conversation, and some provision for obtaining refreshments.
a sitting room (usually at school or university)
Meaning Room used by students for relaxation outside course time.
Room used by students or staff for relaxation.
A common room is a type of shared lounge, most often found in dormitories, at (for example) universities, military bases, hospitals, rest homes, hostels, and even minimum-security prisons. It is generally connected to several private rooms, and may incorporate a bathroom.