What is a MetaBook?
At a guess, a book about a book of the same name. Failing that, just a book about a book (which would then include GoodOmens in the category).
A MetaBook might also contain a MetaStory.
From: HitchhikersGuideToTheGalaxy
Would MetaBook include other fictional books that informed the characters' actions, even if they appeared in books that weren't given the same title? I'm thinking of the JuniorWoodchucksGuidebook?, which featured prominently in the CarlBarks UncleScrooge? comics, or the "Book of Rules" from JackChalker?'s "Dancing Gods" series. - RjLesch
I don't think that qualifies. To be a MetaBook it has to be about the original book. A book merely mentioned in a story is just another prop.
How about...
I nominate "SophiesWorld". Not just a MetaBook, but a book within a book within a book about books within books (not to mention philosophy). -- TomStambaugh
"SophiesWorld" is metafiction which is something entirely different. -- Kevin
I go for "The Dictionary of the Khazars", by Milorad Pavic. Hard to explain if you haven't read it, but worth it. Would Ray Bradbury's TheIllustratedMan? be covered in MetaTattoos? then? -- BrianEwins
How about CliffsNotes??!? --BillSeitz
See also ThisIsTheTitleOfThisStory, DefinitionOfMeta