Enhancement bonus

An enhancement bonus is a specific type of bonus that applies to:
 * AC for an armor that has been magically enhanced
 * Attack and damage rolls for a weapon that has been magically enhanced
 * Attack speed (e.g. from Melee Alacrity items or Haste spell)
 * A specific skill for some spells (like Jump) and some magic items (another kind of skill bonus is a competence bonus)
 * A specific ability for some spells (like Bull's strength) and some magic items

In addition:
 * Weapons that have any + enhancement bonus will bypass DR/Magic.
 * Armor that has any + enhancement bonus is automatically considered Masterwork, and thus has -1 less armor check penalty then a standard set of armor.

Enhancements bonuses do not stack (for instance the bonus given by Dexterous Boots would not stack with the bonus given by the Cat's Grace spell).