Estivation & Hibernation
Estivation is the lessening of the metabolism depending on temperature or climate. This occurs to organisms living in areas of extreme/intense heat. The state the animals go in is similar to Hibernation, except estivation occurs for a short amount of time. Estivation helps a living being that is living in a hot region avoid damage and the risk of desiccation. An example would be a reptile who goes underground and goes through a period of dormancy. This is a time period when an animal's food and water source is low, so this ensures it's survival because they will become temporarily inactive and store energy as they sleep.
Hibernation is a state of inactivity and the lessening of the metabolism. Unlike Estivation, it occurs for a long period of time, and is usually during low temperatures. Hibernation ensures an animal's survival because it lowers their metabolism during a time period when food would be unavailable. Before animals go into this state they must store sufficient amounts of fat that will last the whole season or quantity of time they will be hibernating.