Homeostasis comes from the Greek word, homeo – meaning same and stasis – meaning state. This implies a state of balance in which conditions in the internal environment of living organisms allow them to function efficiently, despite fluctuations in the external environment.
Homeostasis: the maintenance by an organism of a constant or almost constant internal state, regardless of external environmental change.
In order to maintain a constant internal environment there are two essential steps. Firstly, detect the change, secondly, counteract the change.