1. Literally what it sounds like, but a more sarcastic version of itself. As a substitute for "cool", coolios can be used as a joke between friends or as a sarcastic response to something you don't really care all that much about.
2. An adjective, describing how cool and, in some cases, attractive someone else is. A gender-neutral word in this sense.
John: Hey, I got the new game for my X-Box!
Abigail: Guess who I saw walking down the road today? It was Richard!
Amanda: Really?! He is SO coolios!