Dormancy or torpor is a widely recognized behavioral and physiological state of both animals and plants that generally indicates inactivity and reduced metabolic rate. It can involve very different physiological states in response to a variety of environmental stimuli, including temperature, water, or food. It can last <1 day, may occur for a few consecutive days, or may last an entire season or even many years. Torpor involves physiological changes related especially to body temperature, metabolism, and water balance. Hibernation is when an organism spends the winter in a state of dormancy; it is long-term multiday torpor for survival of cold conditions. Estivation is summer dormancy, for survival of hot and dry periods. The general roles of torpor, hibernation, or estivation are avoidance of unfavorable or lethal short- or long-term (seasonal) climatic conditions and conservation of energy during this period of inactivity. Seasonal dormancy allows species to exploit ephemeral environments and colonize habitats that would otherwise be unsuitable for growth or survival at certain times of the year. There are costs to dormancy and torpor, but the advantages contribute to the fitness of individuals and species that use it.