what is death?

Is it when u can't move ur body?
Is it when u can't feel a thing?
Is it when ur heart stop beating?
Is it when u can't breath spontaneusly?
Is it when ur brain stops working although ur heart's still beating?
Is it when u lost ur will to live?
I'm 24 years old. I study medicine. I still seek the answer.
So for those who by accident or not cause death on someone or some people, u may rethink again about how complicated life & death are.
Think before u act.