Rule 615.1 · Prevention Effects
Some continuous effects are prevention effects. Like replacement effects (see rule 614), prevention effects apply continuously as events happen—they aren’t locked in ahead of time. Such effects watch for a damage event that would happen and completely or partially prevent the damage that would be dealt. They act like “shields” around whatever they’re affecting.
Subrules
Effects that use the word “prevent” are prevention effects. Prevention effects use “prevent” to indicate what damage will not be dealt.