The process by which the body's internal environment is kept stable in spite of changes in the external environment is called homeostasis. An example of your body maintaining it's internal environment is that, no matter what the outside air temperature is, your body maintains it's internal temperature as close to 37 degrees Celsius, as long as you are healthy. ( If you are sick, your body may not be able to maintain this temperature, until you become well again.)
Homostasis is the ability of an organism or system to maintain internal equilibrium by adjusting and regulating various physiological processes. It is essential for the body to function properly and keep conditions stable despite external changes.