Life is experiences. Experiences as in feelings.
As long as one has ability to feel he is alive. If something cannot feel he is not alive.
Note that its about ability to feel. One is still alive when unconscious. Its because he is not dead, he didn't loose the ability to feel.
Can a dead body feel anything? Our observations show it don't. Pin it, punch it, burn it, no reaction. Ofcourse we are limited to our observations and to whats told to us if whats told is indeed right.
Muslims are told that though once we are dead we dont feel this worldly things we do feel other things. Pleasures and pains that depends only on our deeds and on God's mercy. The grave part of Life After Death that happens to everybody even if they dont get a physical grave.
Is a stone alive? None of our observations show it is. If your religion says it is only then you will believe it is alive.
In every day speak we say a person is lively if that person is having a lot of experiences in his life. An olympics player, a world traveller, a rock-climber is considered more lively than a regular person.
We say someone's eyes are lively when they show lots of emotions. We "see" a lot going on in that person through his eyes.
Kids are considered more lively than their grandfathers. Kids shows more actions and more emotions. Kids cry, laugh and love without filters.