Gall is a term that can have several meanings depending on its context.
1) In medicine, gall refers to one of the four main types of bile produced by the liver and stored in the gallbladder. Gallstones are hardened deposits of this substance that form in the gallbladder or bile ducts.
2) In a more general sense, gall can refer to anger, irritation, or resentment towards someone or something. For example, "He had too much gall to say such things."
3) Gall is also used as a term for courage or bravery in certain contexts. For instance, one might hear the phrase “gall of heroism” which means having great courage and bravery.