A combo of, "Chill out," and "Relax." It can also be considered a comb of just, "Chill," and "Relax," the same meaning remains.
It can be used to tell someone to calm down, or to describe hanging out. Example: "We should get some beers and just chillax sometime, man."
The word originated in Richmond area Virginia.
Woah, woah, woah, chillax!
Chillax, I mean you no harm.
You and me should get together and chillax sometime.
Chillax, I didn't mean anything by it.
Alright, see you later. Chillax.