In digestion, a bolus (from Latin bolus, ball) is a round mass of organic matter moving through the digestive tract. A bolus is initially shaped through chewing and swallowing of food and maintained as peristalsis moves it through the intestines, eventually being released as feces. The term is also used in aerospace engineering, in order to define the characteristics of human feces, especially pertaining to devices for processing its defecation while in space or other flight environments.

A radio-frequency identification tag ingested by livestock is also referred to as a bolus. It remains in the stomach of the animal for its lifetime and emits a unique ID that can be used to track an animal.