ExcretionExcretion is the biological process by which an organism separates waste products from its body. The waste products are then usually expelled from the body by elimination.
In mammals, for example, the two major excretory processes are the formation of urine in the kidneys and the formation of feces in the intestines. The waste products are eliminated by defecation and urination respectively.
In insects, a system involving Malpighian tubules is utilized to excrete metabolic waste. Metabolic wastes diffuses or is activiley transported into the tubule, which transports the wastes to the intestines. The metabolic waste is then released from the body along with fecal material.