Armor class

In the tabletop role-playing game Dungeons & Dragons, armor class (abbreviated AC) is a number assigned to every character or creature, which indicates how difficult it is to hit that creature with an attack.

In early versions of D&D, a lower armor class indicated that a creature was more difficult to hit (see THAC0). An unarmored human had an armor class of 10, and armor lowered a character's armor class. A more powerful creature usually had an armor class lower than 10.

In third edition D&D, the armor class system was changed. An unarmored human still has an armor class of 10, but now armor increases armor class. In addition, a wider range of factors can affect armor class. Finally, in this system, there is a precise system for assigning armor classes, whereas in earlier editions this was somewhat ad hoc.

Numerous Dungeons & Dragons-derived games use the Armor Class system or a variation thereof. Many games with unrelated systems (such as Fallout) use the term to represent a character's ability to avoid damage.