Homeostasis

Biological processes by which mammals maintain a stable core temperature. This is around 37 degrees Celsius in humans, but it does vary amongst individuals, age ranges, genders, and even time of day (core temperature will naturally drop at night, for example).

Homeostasis is controlled by the hypothalamus in the brain, which controls certain reflexes to increase or decrease temperature (increase/decrease metabolism, cause shivering, burn brown fat, cause sweating, cause discomfort to motivate a change of environment, etc.).