It's a combination of "Nibiru" and "G" from "Google" --> Gibiru.
Nibiru is supposed to be some planet or alien thing:https://www.google.com/search?q=nibiru
Something to do with some alien race - the Annunaki:https://www.google.c...ch?q=anunnaki+nibiru
It all gets into some theory about aliens here on earth, the pyramids, crop circles, religion, and other stuff. No idea what to make of it. It's entertaining anyways. Lots of videos about it on YouTube.