How does excretion differ from egestion in animals?

In biology, the terms excretion and egestion are distinct processes used by animals to manage waste, though they are sometimes incorrectly used interchangeably.1

Excretion

Excretion is the process by which animals eliminate the nitrogenous by-products of metabolism and regulate the composition of body fluids. This process is essential for maintaining homeostasis, as it allows organisms to control osmotic pressure and acid-base balance. The primary metabolic waste product is ammonia, which is derived from the breakdown of proteins. Depending on the animal's environment and water conservation needs, this may be excreted as ammonia, urea, or uric acid.12

Egestion

Egestion is the act of discharging undigested or unusable material from a cell or the digestive tract. Unlike excretion, which deals with metabolic waste produced by cells, egestion involves the removal of bulk food matter that the animal was incapable of digesting or using, such as cellulose. In multicellular animals, this material is typically expelled as feces through the anus.1345