Gallstones are stone-like objects that develop in the gallbladder or bile ducts (the pipe-like system within the liver). Gallstones can range dramatically in size, from tiny grains of sand to golf ball-sized objects. Interestingly, small stones can often cause the most trouble. These are stones that can leave the gallbladder and get stuck.
https://my.clevelandclinic.org/health/diseases/7313-gallstones

