Flatulence is defined in the medical literature as "flatus expelled through the anus" or the "quality or state of being flatulent",[1] which is defined in turn as "marked by or affected with gases generated in the intestine or stomach; likely to cause digestive flatulence."

It is normal for humans to pass flatus through the rectum, although the amount and the frequency may vary greatly between individuals. It is also normal for intestinal gas passed through the rectum to have a characteristic feculent smell, although this too may vary in concentration. Flatus is brought to the rectum by specialised contractions of the muscles in the intestines and colon. The noises commonly associated with flatulence ("Blowing a raspberry") are caused by the vibration of the anal sphincter, and occasionally by the closed buttocks. Both the noise and smell associated with flatus leaving the anus can be sources of embarrassment or comedy in many cultures.