These words denote the section of the human or other animal body between the diaphragm and the pelvic floor. Stomach is the most general term; it may simply mean the external region, although specifically it is applied to the internal digestive organ. As the seat of appetite or inclination, stomach is used figuratively, especially in a negative sense: to have no stomach for strong drink, to have no stomach for the business of killing.

In scientific terminology, abdomen is the word for both the external stomach and for the entire internal cavity containing the alimentary canal and other organs as well to open up an abdomen to remove a tumour; the enlarged abdomen of a woman in advanced pregnancy.

Belly was once a standard word to refer to the same region, but was later euphemistically suppressed in favour of stomach , which is imprecise, and abdomen , which to some people is less acceptable because of its technical sound. Also, belly once meant "womb" or "uterus," as well as the organ which receives food. Perhaps for this reason it is jarring to some ears. From its original meaning of "bag," belly suggests both a hollow cavity and a protuberance: the belly of a sail; his little, round belly tightly buttoned into his trousers.

Unlike stomach , belly or abdomen , guts applies almost exclusively to the internal organs of the pelvic cavity. In the plural, it is a synonym for "entrails" or "intestines," and, in the singular, for the entire digestive system, especially that of an animal. Guts emphasizes the more earthy or even revolting aspects of the intestines when they are not functioning properly or have suffered injury: the sundowner’s guts growling with hunger; a horse in the bull ring with its guts hanging out. Guts has the slang, figurative meaning of courage or effrontery: to have the guts to cross a field under gunfire; to have the guts to insult the managing director of one?firm.

In order to avoid the technical or vulgar uses of the above words, tummy is very common in informal but polite contexts: Hold your tummy in; to have a tummy ache.