locker room

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

• noun A room furnished with lockers, as in a gymnasium, school, or workplace, used as a place in which to change clothes and store equipment.

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

• adjective Characteristic of conversations held in locker rooms; that is, either very informal, boastful, juvenile, or explicitly sexual.
• noun A room attached to an athletic, recreational, or workplace facility, filled with lockers for storage of clothing and equipment; clothes are generally changed there.

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

• noun a room (as at an athletic facility or workplace) where you can change clothes and which contains lockers for the temporary storage of your clothing and personal possessions