urinary bladder

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

• noun An elastic, muscular sac situated in the anterior part of the pelvic cavity in which urine collects before excretion.

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

• noun anatomy An elastic, muscular sac situated in the pelvic cavity, into which urine from the kidneys is stored prior to disposal by urination. Urine enters the bladder via the ureters and exits via the urethra.

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

• noun a membranous sac for temporary retention of urine