Armor bonus

Armor bonus is a bonus to Armor Class granted by armor or by a spell or magical effect that mimics armor.

Armor bonuses stack with all other bonuses to Armor Class (even with natural armor bonuses) except other armor bonuses.

Magic armor typically grants an enhancement bonus to the armor's armor bonus, which has the effect of increasing the armor's overall bonus. An armor bonus granted by a spell or magic item typically takes the form of an invisible, tangible field of force around the recipient.

An armor bonus doesn't apply against touch attacks, except for armor bonuses granted by force effects (such as the mage armor spell) which apply against incorporeal touch attacks, such as that of a shadow.