The extended version of OMG (oh my god/gosh/goodness). But, you may be asking, doesn't extending an acronym in text talk defeat its purpose? Yes, yes it does.
A hyper-exaggerated version of the exclamation OMG. Used when one's level of excitement is so high, that it's like gumdrops, glitter, hearts, moonbeams and My Little Ponies are exploding out of your mouth as you are talking about it.