noun
binding margin; gutter; seam allowance
Refers to the extra space left along the edge of a page or fabric for binding or sewing. In bookbinding it is the gutter margin; in sewing it is the seam allowance.
印刷するときは、綴じ代を十分に取ってください。
When printing, please leave enough binding margin.
この本は綴じ代が狭いので、コピーしにくい。
This book has a narrow gutter, so it's hard to copy.
縫い代 specifically refers to the seam allowance in sewing, while 綴じ代 can refer to both sewing and bookbinding margins.
Compound of 綴じ (とじ, continuative form of 綴じる 'to bind') + 代 (しろ 'allowance, margin').