Armor-Based Weapon Resistance
When a weapon attack is a Glancing Hit (but not a Full Hit), your armor grants you 50% Resistance to the weapon damage suffered. Certain powers and abilities may overcome your Armor-Based Weapon Resistance, in which case you suffer full damage even if the attack does not surpass your Hit AC.
Armor-Based Weapon Resistance can only reduce Weapon-type damage (i.e. Bludgeoning Damage, Chopping Damage, Piercing Damage, and Slashing Damage), and therefore does not have any affect on Energy or Alignment damage dealt by Weapon Attacks. If an attack deals both Weapon-type damage and Damage of another type (i.e. fire, poison, holy, etc), the portion of the damage of the Weapon-type is still reduced on a Glancing Hit.