Trim size.

The size of the printed book as it leaves the guillotine. KDP defines it as the book's width and height, and every other measurement in the file is set from it. A page that carries bleed is larger than the trim: KDP adds 0.125 in to the width and 0.125 in at top and bottom, so a 6 x 9 in book gets a 6.125 x 9.25 in page, and the blade takes 0.125 in (3.2 mm) from the top, bottom and outside edges. IngramSpark defines bleed as the area beyond the edge before trimming, lets a file with no bleed be submitted at trim size, and asks for 0.125 in of bleed on the three outer edges of an interior. The page size is therefore not the book size, and one export reused across platforms is wrong at every platform but one, because each adds its own bleed. The usual fault is a file built at the trim size with art that runs to the edge, so a white sliver shows on one side of some copies.