Gallstones and bile duct stones are solid, pebble-like deposits that form in the gallbladder or bile ducts. Gallstones are formed from bile components, such as cholesterol and bilirubin, in the gallbladder, while bile duct stones can form in the bile ducts or migrate from the gallbladder. These stones can cause blockages, leading to pain, inflammation, and infection in the abdomen.