After decades of biological research, we're still not sure what makes an organism alive, in the sense that the line between living organisms and inert biological material is not well-defined, but we know how living organisms reproduce and grow, and that's really what matters.
It might be as simple as "it's alive while it's a functioning machine." A disassembled car is just parts and can't drive/be-alive, but assembled it is a car and can drive/be-alive.