Ectotherms are organisms that rely on external sources of heat to regulate their body temperature. They cannot generate their own body heat like endotherms (warm-blooded animals) do.
Related terms
Endotherms: Animals that can internally regulate their body temperature by generating heat through metabolic processes.
Thermoregulation: The process by which organisms maintain a stable internal body temperature.
Hibernation: A state of inactivity and reduced metabolism used by some ectothermic animals to survive cold temperatures or scarcity of food.