Living  VS. Non-Living
Living things carry out almost all the life processes or activities.   These life processes include digestion, respiration, circulation, excretion, locomotion, immunity, coordination, and synthesis.   Non-living things are incapable of carrying out at least one or more of the life processes.    The sum of the energy used in all the life processes represents the metabolism of the organism.   

Homeostasis
The ability to carry on the life processes allow a living thing to maintain dynamic equilibrium or homeostasis with their surroundings.   Homeostasis is a state of balance or steady state between a living thing and its environment.   Homeostasis in an organism is constantly threatened.  Failure to respond effectively to a failure of homeostasis can result in disease or death.