A word used to express disbelief, or strange unintelligible feelings usually related vaguely or directly but not limited to surprise, anxiety, excitement, pocky. Can be used in place of "dirty words" around your mother or the higher brow community to avoid ridicule and crude embarrassment.
May also have something to with a strange theatre costume . . . this is unconfirmed at the present time.
"Dude did you just see that elephant do a backflip?"
"What the Shua?! Impossible!"
--- and also ---
Shua! I just stubbed my foot!