gallbladder in Medicine Expand. gallbladder or gall bladder. n. A small, pear-shaped muscular sac, located under the right lobe of the liver, in which bile secreted by the liver is stored until needed by the body for digestion. Also called cholecyst, cholecystis. gallbladder. A small, pear-shaped muscular sac in most vertebrates in which bile is stored.