A defensive bonus directly affects defensive strength (DS). In its most common form--on armor and shields--it is equivalent to the item's enchantment.
In rare cases, other wearable items, such as clothes, shoes, and jewelry, were given defensive bonuses; these items are known as DB items.
Temporary defensive bonuses are available in the form of a wide variety of defensive spells. There are many such spells, and the most common ones include Spirit Defense (103), Mass Blur (911), Mass Elemental Defense (419), and Mass Colors (611).
A defensive bonus can also be granted by a rare enhancement found on some weapons (known as defender weapons). The defender bonus on a weapon takes up the same Category B property slot as standard flares or ability to bless.
For both defender weapons and DB items, creation of and adding to the bonus is a very rare merchant service.
Behind The Scenes
The term "DB item" originated in the Rolemaster system used in the ICE age and the terms OB vs. DB rather than AS vs. DS.