I've been meaning to ask....

Well, Annwfn is the proper Welsh spelling of "Annuvin", the land of magic and myth that exists outside our own. More recently (and popularly), Annuvin is the homeland of the evil King Arawn from Lloyd Alexander's "Chronicles of Prydain".

Note that even in Welsh mythology, Annwfn isn't a very happy place; the closest parallel in our Judeo-Christian mythology is Hell. So you *could* read it roughly as "The Hounds of Hell".

Just to answer in writing:

Annwfn, also called the "twilight land," is the place where (in the Tain and other Gaelic mythologies) the Hunter lives with his terrible hounds. These hounds are white with red ears, and run through the sky chasing the souls of the damned every harvest-time (around Halloween.) You may remember his appearance (with his hounds) in Silver on the Tree by Susan Cooper. Annwfn is not the place where the dead go, but is a sort of no-man's-land between the world of the living and the world of the dead. It is said that through it one might find the door to Tir na Nog, the land of eternal youth and beauty, where the souls of the dead DO end up.

You generally end up in Annwfn by chasing an elusive creature (a white stag, etc.) farther than you've ever hunted before. Fog will close in, and you will be in the twilight land. Should you meet the king there, as the kings and queens in the great mythological epic The Tain did, he may offer to take your place in the real world in exchange for his place in Annwfn.

Does it matter? It's FREAKIN AWESOME. That's all I care about.