Stands for "Wa Da Ma Ya," which literally translates to "Oh my mother," in Chinese.
It is used similarly to "Oh my God (OMG)," "Oh my fucking God (OMFG)," "Oh my word," "Oh my Goodness," "What the Fuck (WTF)"
"What the hell (WTH)," etc.
"Holy-cat-scaling-a-building Batman!"
"WDMY!"
