The term AP when used in World of Warcraft can refer to one of two things. Most often it means attack power, a stat that increases damage done by melee and ranged attacks. Attack power is a stat on many items designed for physical DPS characters. Every 14 points of AP will increase your base damage per second by 1. This usually ends up increasing your actual damage per second by considerably more, thanks to special attacks and increased attack speed. Attack power is obtained from strength by all classes, agility by rogues, cat druids, shamans, and hunters, and intellect by hunters and shamans if they have the correct talents.
AP can also sometimes refer to armor penetration rating. Armor penetration lowers an enemy’s armor value, allowing your physical damage attacks to deal more damage. The AP WoW term’s definition is well-known among players, especially ones who play physical DPS characters.