Thompson used to be a sports writer. He was sent to the desert to write a piece about a dune buggy race, but he was so stoned, drunk, and screwed up, the copy he eventually turned in had little to do with the race, and lots to do with the Doctor's inability to cover the story due to the "hardships" (self-imposed and otherwise) he faced along the way. The editor published it as-is, and a new form of "journalism" was discovered.
But still, what is this word? How did it even come about?