What is the process by which the body maintains a stable internal temperature?

The process by which the body maintains a stable internal temperature is thermoregulation.

In humans, thermoregulation is controlled mainly by the hypothalamus, a brain region that acts like a thermostat. Temperature sensors detect changes in the blood and skin, prompting responses such as sweating, shivering, widening or narrowing of skin blood vessels, and changes in behavior.

Thermoregulation is one part of homeostasis, which means maintaining stable internal conditions generally. Homeostasis is therefore broader than temperature control. Metabolism contributes to heat production, while osmoregulation controls water and salt balance; neither term specifically names temperature regulation.

Humans are endotherms because much of their body heat comes from internal metabolic activity. The body still exchanges heat with its surroundings through radiation, conduction, convection, and evaporation, especially when sweat evaporates from the skin.