stomach
An exposed frontal abdomen, specifically the area around the navel and above the groin. For images pertaining to the internal organ itself, use stomach_(organ).
Should only be used when the stomach is a prominent, noticeable part of the image, not merely in the background or partially exposed.
Unlike midriff, stomach can be used when the stomach is visible between underwear, bikinis, and when the character is nude, bottomless, or topless female/topless male.