Homeostasis and its role in the functioning of living organisms as non-equilibrium thermodynamic systems have been carefully investigated. The author tends to prove that homeostasis remains as a desire of a living organism to be closer to an optimal equilibrium thermodynamic state, depending on the conditions of its functioning. Simultaneously, a few definitions are clarified, such as the principle of life activity of living organisms, a living organism, life, the purpose of life, as well as the property of loss and restoration of functions.