Definition of "OMG"

I hear that a new order of Knighthood is on the tapis—O.M.G. (Oh! My God!)—Shower it on the Admiralty!!

1917 September 9, John A.F. Fisher, letter to Winston Churchill

10 Bands, 50 bands, 100 bands, fuck it, man / Let's just not even discuss it, man / OMG, niggas sleep, I ain't trippin', I'ma let 'em sleep

2015, “10 Bands”, in If You’re Reading This It’s Too Late, performed by Drake