'Fold' in the Bible

'Verily, verily, I say to you, He who is not entering through the door to the fold of the sheep, but is going up from another side, that one is a thief and a robber;

And other sheep I have, which are not of this fold: them also I must bring, and they shall hear my voice; and there shall be one fold, and one shepherd.

But you do not believe Me [so you do not trust and follow Me] because you are not My sheep.