The 2 best definitions I've heard come from Earl Nightingale, describing it as, the progressive realization of a worthwhile goal. The other from John Wooden who said, it's not about being better than anyone, but being the best you are capable of becoming.
I was reading a devotion from David Jerimiah and he had a Henry Ward Beecher quote. No man can tell whether he is rich or poor by his ledger. It is the heart that makes a man rich. He is rich or poor according to what he is, not according to what he has.
How about you, heard any other definitions, or one of your own. Please share if you have.