Homeostasis is the capacity of an open system to regulate its internal environment to preserve a steady condition by means of multiple dynamic equilibrium adjustments forbidden by interrelated regulation mechanisms. All living organisms, whether multicellular or unicellular, exhibit homeostasis. Homeostasis exists at the cellular level, for example cells keep a stable internal acidity; and at the stage of the organism, for example warm-blooded animals maintain a stable internal body temperature.

Homeostasis is a term that is also used in involvement with ecosystems, for example, the atmospheric concentration of carbon dioxide on Earth has been regulated by the concentration of plant life on Earth because plants remove more carbon dioxide from the atmosphere in the daylight hours than they produce to the atmosphere at night. Hankies and organs can also keep homeostasis.