Flatulence is the expulsion of gas from the intestines via the anus, commonly referred to as farting. "Flatus" is the medical word for gas generated in the stomach or bowels. A proportion of intestinal gas may be swallowed environmental air; hence, flatus is not entirely generated in the stomach or bowels. The scientific study of this area of medicine is termed flatology.
Passing gas is a normal bodily process. Flatus is brought to the rectum and pressurized by muscles in the intestines. It is normal to pass flatus ("to fart"), though volume and frequency vary greatly among individuals. It is also normal for intestinal gas to have a feculent or unpleasant odor, which may be intense. The noise commonly associated with flatulence is produced by the anus and buttocks, which act together in a manner similar to that of an embouchure. Both the sound and odor are sources of embarrassment, annoyance or amusement (flatulence humor). Many societies have a taboo about flatus. Thus, many people either let their flatus out quietly or even hold it completely. However, holding flatus inside the bowels for long periods is not healthy.