Defining high risk/high payoff

Click on the link above for the mandate from the US Congress to NSF on funding more high risk research.

And what constitutes “high risk”?
“Research driven by ideas that have the potential to radically change our understanding of an important existing scientific or engineering concept, or leading to the creation of a new paradigm or field of science or engineering, and that is characterized by its challenge to current understanding or its pathway to new frontiers.”