abstract:An endotherm (Greek: endon = "within", thermē = "heat") is an organism that maintains its body at a metabolically favourable temperature, largely by the use of heat set free by its internal bodily functions instead of relying almost purely on ambient heat. Such internally generated heat is mainly an incidental product of the animal's routine metabolism, but under conditions of excessive cold or low activity an endotherm might apply special mechanisms adapted specifically to heat production.