We can define life in terms of proactivity and free-will. The clear difference between living entity and a lifeless one is that for the same exact triggers at the same conditions the lifeless entity have only one single response that can’t be changed every time the same trigger arises, while living entites are not bound to a single response to a trigger at the same conditions. They have the free will to chose how to respond and they have the ability to make experience out of past feedbacks which allow them to choose a dufferent response each time and this is how they develop.