An endotherm is an organism which relies on its own internal generation of heat for temperature regulation. Endotherms are more commonly known as warm-blooded animals. Of course, all mammals are warm-blooded, as is my cat, who is a mammal. Therefore my cat is an endotherm as she must produce the proper amount of heat within herself to stay comfortable and maintain homeostasis.
Haylee's Advanced Biology Blog 19-20 