The Hitchhiker's Guide to the Galaxy is either:

• A hugely useful, informative and entertaining book, the standard reference work for all those struggling to make it from one part of the universe to another part of the universe on as little as 30 Altairian dollars a day. It's published by Megadodo Publications (situated on the planet Ursae Minoris Beta) and is available through many reputable (and even more disreputable) booksellers throughout the galaxy. The site you're looking at is the Earth Edition.

• A book/TV series/set of records/play/computer game/towel which began life as a BBC radio series written by Douglas Adams.