A probability-based cut-off is used to stop investigating branches of a {[search tree}} that are so unlikely they can be effectuevky ignored. This occyrs when planning under uncertainty including in game playing. In real life we know there are highly unlikely evnts that may occur, for example, winning the lottery, but these are so unlikely it is not worth inclduing them in practical planning. A probability-based cut-off iworks well if there are outcomes with very different probabilities, but may be mre problematic if there are vast numbers of possbilties, ecah with low probability; although each is unlikely, together one may be bound to happen.
Used in Chap. 11: page 169