What exactly is The Hitchhikers Guide to the Galaxy?

The Hitchhiker's Guide to the Galaxy concerns the exploits of Arthur Dent, an average British citizen who gets caught up in a myriad of space adventures when his house, and then the Earth, is demolished. With no planet to call home, he is left to hitchhike through space with his friend Ford Prefect, whom he thought was an outof-work actor, but who is really a researcher for the intergalactic guidebook named in the title. Adams's book is one in which literally anything can happen, with the only rule being that what comes next will probably be the last thing the reader would expect and is bound to be amusing.