At a frontier node (one ply away from quiescence), if the static evaluation plus some margin is less than alpha, proceed straight to quiescence or even return an evaluation immediately.

Works best in combination with lazy evaluation.

Lower margins give a faster - but less accurate - search.

If the margin is larger than the maximum possible score improvement, futility pruning is completely theoretically sound but does not prune anywhere near so many nodes.

Futility Pruning