The final in the:
O Rly, Ya Rly, No Wai sequence.

shorter version of `really`.

The opposite of "ya rly," yet another possible response to "o rly?."

(adjective) really, extremely, very

A way mentally slow people spell the word "really." It appears only people with an IQ lower than the average human's temperature uses this "abbreviation." Yeah, and I'm the King of Egypt.

meaning not really, used by people too slow to type whole words, also abbreviated to "nt rly".
alternate response to the question "ya rly" which is all too common internet slang.

1/2 Chatspeak,1/2 sarcasm.
This phrase is often used when someone makes a dumb comment of disbelief to a statement.