It's a word that you say when you're not kidding.

Zynga! Yes, I really am trying to patent the obvious, with loads of prior art.

Its opposite is "bazinga", which means "I was kidding".

I asked a patent office employee about this. Apparently, a thing is only prior art if it is patented itself, or is published in an accepted academic journal, and then only if such things can be found in the ten hours the examiner is given per patent application.