All attacks in Tyranny compare the attacker's Accuracy value to one of five defenses: Parry (direct melee attacks), Dodge (direct ranged attacks), Endurance (body system attacks like Stun and Prone), Will (mental attacks), and Magic (attacks from spells and spell-like abilities).
Accuracy is defined primarily by the attacker's skill with that type of attack (weapon skills for physical attacks, magic skills for spell attacks, etc.). It can be influenced by Finesse, Talents, and other active effects such as spells or items.
When an attack is made, the attacker's Accuracy is compared to the appropriate defense on the target to determine how the attack roll will be modified. If Accuracy is above the target's defense, it will be more likely to result in a Hit or Crit, less likely to result in a Graze or Miss.