Used to show anywhere from excitement to disgust in a situation. It's a short word that can be used to show just about any kind of expression! If you want to spice up "wow" a little bit, this is the word to use.
Wife: I just saw our future new neighbors fighting on their front porch already!
Husband: YOWZA, that's just great!
Girl 1: Did you hear about ladies night this Saturday where the women drink for free?