Final answer:
The term for when an organism slows its body systems during cold temperatures is hibernation, which is a state of torpor allowing survival with lowered metabolism.
Step-by-step explanation:
The term used to describe when an organism slows its body systems during periods of cold temperatures is hibernation. Hibernation is a form of torpor that occurs over long periods, such as winter, making it possible for animals to survive with a significantly lowered metabolic rate.
For instance, during hibernation, an animal's body processes slow down, and its body temperature falls, allowing it to use less energy at a time when food might be scarce. Contrary to hibernation is estivation, another form of torpor, which some animals use to survive the hot and dry conditions of summer.