Critical hit

On a critical hit rolled damage is multiplied by the critical hit multiplier listed on each weapon after the threat range.

If you hit your target while getting a (non-modified) d20 roll within your weapon's threat range, this results in a critical threat, i.e. a chance for a critical hit. A (currently hidden) additional attack roll is made, and if it results in a hit, the critical hit is confirmed and the base damage you inflict to your target is multiplied by your weapon's critical hit multiplier. Note that the second roll does not need to fall within the threat range, it just needs to be enough to hit your target.