The Brief: An expression meaning "Oh my God" or "Oh my goodness," to indicate a surprise or shocked emotion.

DEEP DIVE
OMG stands for “Oh my God” or “Oh my goodness.” It’s commonly used in texts or tweets to denote a shocked or excited emotion. It can either be written in all caps, or lowercase as “omg,” to convey a less dramatic tone. A variation of the expression is ZOMG. OMG has been used in memes like “me on Ellen,” where a guest on Ellen DeGeneres’ show is overwhelmed by the host’s absurdly grand surprise gift.
me on ellen
ellen: so i heard you love the ocean
me: ya
(the studio starts flooding)
me: omg ellen you didnโt
— ari (@darlingadora) March 2, 2019
i bought my cats these hats omg pic.twitter.com/2FUx5jWmkJ
— justine (@biticonjustine) March 13, 2019
OMG ANGEL pic.twitter.com/f1n2FLVW2x
— Rachel (@13swift1989) March 14, 2019