folded in the middle; center fold
Describes something that is folded or creased at its center. Often used for hats, paper, or other flat objects.
I folded the paper in the middle and made a booklet.
Please fold this paper in the middle and put it in the envelope.
Compound of 中 (naka, 'middle') and 折り (ori, 'fold'). The exact historical derivation is uncertain, but the meaning is transparent from its components.