When you save a new iWork document under Mountain Lion you are given the default extension of .pages-tef or .numbers-tef. These files appear to be directories and a different format than your standard .pages or .numbers file (I haven't had the chance to create a new Keynote preso yet).
Does 'tef' stand for anything? Are these just 'iCloud compatible' files and they've been dubbed '-tef' as the extension? Apple isn't one to name things without a specific intent and nothing specific comes to mind.