What is life?

Glimpses to the past lead me through envisages of my life experiences of 21 years.Still this question haunts me. Well perhaps everyone might be having this question or it hasn't been the time to many to ask the question.
What we need to live?
Food? water? or the price society puts on your neck?
Didn't knew the dictum "Man is a social animal" will get into his head so much.

But still, I believe we must make some mark on this world before exiting.