What is the definition for life?

Though I am a programmer, sometimes my mind becomes a bit philosophical. One day I was wondering about a very complex question. What is the definition for life?. There are some definitions such as "Life is full of ups and downs!", "Life is this","Life is that" and so on...
I am not concerned about the life that we live, but about something that keeps us alive or that makes other say that "He is alive". When someone dies, we know that he is losing something from this body. Not something that we can see or touch. But something more to it.
We cannot say that life is something centered around or inside a particular organ. Because, when brain is dead by stroke or something, we can still keep a person alive by supporting his other vital functionality.Similarly if heart stops pumping, we can even replace it and the person can live for a long time.
So what is life?. What is this thing that we loose when we are dead?. After pondering for a long time,I derived at a conclusion.

My Theory about Life
According to me "Life" is a coordination between the organs. The coordination between different organs can be classified into vital and non-vital. We can say that the coordination link between the heart and brain is a vital link, but that between the hand or legs could be considered non-vital. So when we are amputated, we can still live though with a decreased efficiency, but when vital coordination link with heart or brain is down, we could say that is something  Life threatening. So when this coordination link is completely down, we can say that the person is dead. Hence we can compare the "Life" as a coordination within the body that helps us with each day.