When a single attack made against a character exceeds that character's Fortitude Defense, that character suffers a Wound. A character with one Wound is -1 to all attacks, ability checks, skill checks, and defenses.
If a character suffers additional Wounds, each Wound suffered after the first doubles the penalty. So, a character with two Wounds is -2 to all attacks, ability checks, skill checks, and defenses, while a character with three Wounds is -4. A character with four Wounds is -8, and a character with five Wounds is helpless (either unconscious or disabled).