common room

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A room used for informal gatherings and relaxation, as in a residential institution or a department in a university.

from the GNU version of the Collaborative International Dictionary of English.

• noun 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun UK, Canada, New Zealand A shared lounge found in dormitories, universities, military bases, etc.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a sitting room (usually at school or university)