Very much like the word pie, it can answer any question, break awkward silences and can be used as an exclamation of joy, among other things...
Person 1: Pachow!!!
Person 2: Erm... What?
Person 1: Yep... That's right... Pachow.
Person 1: Yeah!!! Pachow!!!
Person 1: What is the numerical value of pi?
Person 2: Pachow...
Person 1: lol what?
-end of question-