This phrase, in perfect grammar is "Oh Really?", but in online lingo, you type it as "o rlly". This is mostly used when you are kind of shocked in a lollerskating kind of way.
It's ofc the abbreviation of "Oh really" It's used by lazy people 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