The stomach was a type of organ used to digest food, found in the digestive systems of many species.
Lurians have two stomachs, and could use their second stomach as a storage vessel - Morn once kept a large quantity of latinum in his. (DS9 episode: "Who Mourns for Morn?")
In 2254, Number One compared the interior of a Ngultor ship to being inside a giant stomach. (EV comic: "Flesh of My Flesh")