Background: The Bible speaks of sheep and lambs, and 'other sheep', both of which are apparently (?) Christians - they ARE sheep, so does this necessarily make them Christians?  Jesus said "and other sheep I have, which are not of this fold.  Them also I must bring, and there shall be one fold, and one shepherd of the sheep."

Q: who are the other sheep?  We already know they are Christians, but 'not in the fold'.
Q: which fold?

A: it is said in commentaries that the reference to other sheep is to the Gentiles.