A much more fun way of expressing the adjective/adverb "seriously."
People should try it at least once in their lifetime; toss it out there. And, while you're at it, try out other non-words like "foo" and "jank." They make life so much more entertaining, at least for oneself if not for anyone else.
I mean, sirusly, you have to see Hocus Pocus. It's a rite of childhood.