Combat power Combat power makes you hit harder and increases your health for every rank up you get it.
Combat power is a hidden "ranking" of your individal stats, all of which combine into a higher number. There are numerous ways to prevent Combat Power from increasing (main reason for being to train windmill on zombies, etc...) such as CP lowering Armor (enchant specific.)
For the person that got "Combat Power" confused with "Combat Mastery," please play the game more before you post something. Thank you.