What characteristic of life best describes the process of homeostasis?

The best example that describes the homeostasis is the control of body temperature !

homeostasis is the property of a system in which a variable (for example, the concentration of a substance in solution, or its temperature) is actively regulated to remain very nearly constant. This regulation occurs inside a defined environment (mostly within a living organism's body).

as relation to the organism body :

the endotherms and ectotherms are two basic group of organism which is related to homeostasis ! the organism that can control its body temperature is endotherms and so we can say it can have the ability of homeostasis !