Final answer:
Homeostasis is the maintenance by an animal of a relatively constant internal environment in a varying external environment. It is essential for survival and proper functioning of organisms.
Step-by-step explanation:
Homeostasis is the maintenance by an animal of a relatively constant internal environment in a varying external environment. All living things are able to maintain a more-or-less constant internal environment, keeping things relatively stable on the inside regardless of the conditions around them. This process is essential for survival and proper functioning of organisms.