The bladder is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters the bladder via the ureters and exits via the urethra. The typical adult human bladder will hold between 300 and 500 ml (10.14 and 16.91 fl oz) before the urge to empty occurs, but can hold considerably more.

The Latin phrase for "urinary bladder" is vesica urinaria, and the term vesical or prefix vesico - appear in connection with associated structures such as vesical veins. The modern Latin word for "bladder" – cystis – appears in associated terms such as cystitis (inflammation of the bladder).