Feces, also called excreta and stool, are the waste products of digestion. They take form as they are moved along the large intestine by involuntary muscular contractions called peristalsis (see also digestion). The normal daily stool of human adults is about 250g (9 oz). Besides food products, up to 20 percent of this weight is intestinal bacteria. Other constituents are digestive secretions, enzymes, fats, cell debris, electrolytes, water, and small amounts of protein.

The characteristic odor of feces is caused by certain organic chemicals, primarily skatole. Medical examination of feces aids in diagnosing many gastrointestinal disorders. Very dark stools, for example, may indicate an ulcerative lesion in the higher digestive tract. Heavy, fat-rich stools can indicate various intestinal and pancreatic disorders, and so forth. Feces are also examined to detect internal parasites.