Flatulence is the expulsion through the rectum
The rectum is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long...

 of a mixture of gases that are byproducts of the digestion process of mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s and other animals. The medical term for the mixture of gases is flatus, informally known as a fart, or simply (in American English
American English
American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....

) gas. The gases are expelled from the rectum in a process colloquially referred to as "passing gas", "breaking wind" or "fart
Fart is an English language vulgarism most commonly used in reference to flatulence. The word "fart" is generally considered unsuitable in a formal environment by modern English speakers, and it may be considered vulgar or offensive in some situations. Fart can be used as a noun or a verb...

ing". Flatus is brought to the rectum by the same peristaltic
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...

 process which causes feces to descend from the large intestine.