Ectotherms are organisms that rely on external sources of body heat.
Endotherm: An organism that generates its own body heat internally, much like a battery-powered device.
Poikilotherm: An organism whose internal temperature varies considerably. It's like a chameleon changing colors based on its surroundings.
The process by which animals maintain an optimal body temperature, similar to how you would adjust your home's thermostat to keep it comfortable.