(1) (physiology) The catabolic process in the digestive tract where ingested food is converted into simpler, soluble and diffusible substances that can be assimilated by the body
(2) (microbiology) The process of decomposing organic matter through microbial activity
(3) (medicine) Suppuration
In physiology, digestion pertains to the mechanical and chemical processes to break up food into smaller or simpler constituent parts that can be absorbed or assimilated.
Different organisms utilize different ways to digest food. Some organisms employ external digestion whereas others use internal digestion. Many fungi, for instance, use external digestion in which food is digested from the outside through secreting enzymes that degrade food material and then absorbed through diffusion. With internal digestion, organisms digest their food in a closed system such as through the digestive tract, as in those of many animals.