What is attack power for at World of Warcraft?

Answer 1

All classes have a way to increase the damage that they do. For melee classes, this is Attack Power (AP). They more AP that you have, the more damage that you do each attack.

For Hunters, you need Ranged Attack Power (RAP). This is because hunter's do not use melee attack power. Hunter's get this mainly from agility, and some gear.

For casters/healers it is Spellpower (SP). This is mainly received from talents and gear. SP also helps healers in that the more SP that they have the more they heal each time.