It's ofc the abbreviation of "Oh really" It's used by lazypeople or for people "don't like to write"
In worst of cases it can be used by "Toxic" people.
Brother1:Hey Mich! I've went to a restaurant!!
Brother2: Orlly? ...and i'm not mich. And so mom it's mad at you.. also... Why did you went wom?
Brother1:OH NO IM F*CKED