A gallstone is a small, hard deposit that forms in the gallbladder, a small organ located beneath the liver. These stones can vary in size, from a grain of sand to a golf ball, and are made up of substances like cholesterol or bilirubin. When the gallbladder doesn't empty properly, these substances can crystallize and form gallstones, which may cause pain or discomfort. Many people with gallstones experience no symptoms, but when they do, it can lead to a condition called biliary colic. This pain often occurs in the upper right abdomen and can be severe. In some cases, gallstones may require treatment, such as medication or surgery, to remove them and alleviate symptoms.