2. Oh my god.
3. O mah gawd.
4. When used by people with grammar skills, it is often in mocking.
Definition 1: OmG dId U c WaT hApEnEd LaSt WeDnSdAy!!!!!11111
Correct Response - "Speak proper, or STFU, N00B!"
Silent then proceeds to sock her in the face.
Simply put OMG means, Oh my god!
Person 2: "O M G. , have they even heard of the word fashion."