The practice and/or lifestyle of not taking shit from anyone.
It is synonymous with not "selling out" one's principles or sense of self in any given situation, no matter what the cost.
Steven Seagal is the number one proponent of no-selling. In fact, one might describe him as the "living god of no-selling".
I don't care about your money; I just care about the little squirrels... that's what happens when you ask me to sell out... Mission Accomplished!