Final answer:
Hibernation is the term that describes the condition of a desert mouse that lowers its metabolic rate and "sleeps" during the hot day.
Step-by-step explanation:
The term that describes the condition of a desert mouse that lowers its metabolic rate and "sleeps" during the hot day is hibernation. Hibernation is a state of dormancy where an animal's metabolic rate decreases significantly to conserve energy during periods of extreme temperatures or scarcity of food. It is a survival strategy that allows animals to endure harsh environmental conditions.