In my opinion extra-biblical is different than apocrypha, but it's not the same as every-other-book, like books written about Mohamed in 700 AD. What defines a book as extra-biblical for the purposes of tagging questions? (it it even a necessarily a book? my shoes are extra-biblical).
The extra-biblical tag is for secular historical records. But it really only makes sense to use it for questions asking for records from roughly the same time period as the Biblical texts.
After pondering the dark wander's answer for a minute or two, I think I'd like to offer up the option that it is completely useless to us as a tag and should be nuked.
If there are to be questions about works sacred to the various sects and faith traditions, they should be tagged with what they are, not using the blanket tag extra-biblical. I don't think there are any sacred works that wouldn't merit their own tag and the existence of a nebulous tag is confusing.
It's for Christian Sacred texts that aren't argued to be a part of the Bible by the people using them. So it doesn't apply to the apocrypha or The Ethiopian Book of Josippon, but it would apply to the Book of Mormon (although we already have another tag for that), the Didache, and other such works held to be sacred, yet not a part of Biblical canon, by a group of people identifying as Christians. Obviously this tag only is meaningful for groups where the Bible is somehow distinct from the set of all doctrinal sacred writings for that group.