A cry out of awesomeness, satisfaction or accomplishment.
Can also nonchalantly pronounced, slightly wearily.
"I just tied my shoelaces, kapow!"
"Amsterdam is just kapow!"
Looking in the mirror. "Kapow!"
Often accompanied by the "hit-it" hand signal.
Also has many derivitives or shortened versions used to express more than just a hot lookin' fanny. Such as: Pow, Powzer, Powpowpow, ect.