A fold sewn into fabric to shorten or shape a garment; a common dressmaking term.
I adjusted the length of the skirt by putting a tuck in the hem.
Compound of 縫い (nui, 'sewing', the continuative form of 縫う) and 揚げ (age, 'raising', from 上げる). Literally 'sewing up', referring to the action of folding and stitching fabric upward.