What is the meaning of life in one word?

Utility

Life is the opposite of death, like motion is the opposite of stillness. So life is all about doing, so it's all about optimizing a function that as humans we call " utility ", which is the mesurement of the capacity to do with efficiency.

* why do other people act like that? Because it's useful for them.
* why do we see that bacteria motion/behaviour? Because it's useful for her.
* why do a big forest fire is sad? Because it brings stillness where motion was.
* etc...