inner pleat; inner tuck; fabric raised inside to adjust length
A tailoring technique used in kimono and yukata: excess fabric is folded up and stitched inside to shorten the garment while keeping the outer appearance neat. The term is domain-specific to traditional Japanese clothing.
I had the inner tuck of my kimono adjusted.
For a child's yukata, you adjust the length by making an inner tuck.
Compound of 内 (uchi, 'inside') and 揚げ (age, 'raising' or 'tucking up'). The term directly describes the action of raising fabric from the inside.