Typically used with: Self-Control.
In short: body control. Resilience is a measure of a character's inner fortitude, the ability to shrug off mutations, which are spells or powers which distort a target's body. Any supernatural phenomenon which physically distorts a character's physical being is opposed by a Resilience check: shape shifting, petrification, disintegration, or psychokinetic clothing removal.
Resilience checks are always in opposition to another roll or effect, so there are no set difficulties.
Resilience checks are regularly used to oppose some Magic Spells and similar effects.