Definition
Signature
A signature is a large printed sheet folded into a group of pages — commonly 16 or 32 — that is then bound with others. It is why traditionally printed books run to page counts in multiples of 16.
Presses print many pages at once on one sheet, in an arrangement calculated so that folding delivers them in reading order. That imposition is where the multiples come from, and why traditionally printed books often end with blank leaves: the text ran out before the signature did. Digital print-on-demand prints and cuts differently, so the constraint mostly disappears — but it still shapes what a book is expected to look like.
Related tools & guides
Measure yours
Drop an interior PDF into the free KDP checker: it detects the trim, measures the inside margin on every page against the gutter your page count needs, and names the pages that fall short.