A shield bonus is a specific class of bonus to Armor Class normally provided by shields. Multiple shield bonuses do not stack. Note that Two Weapon Defense is not treated as shield bonus in DDO.
Shield bash causes the player to reliquish this bonus thus reducing their Armor Class unless they have the Improved shield bash feat.
Sources of shield bonus:
- Class abilities
Other common bonuses to your armor class are armor bonus, deflection bonus, dexterity bonus, natural armor bonus, and miscellaneous bonus.