What are creep and shingling?
Shingling is usually caused in saddle-stitched publications, where the inner spreads (called "signatures" by press folk) are longer than the outer spreads when folded, because of paper thickness (see illustration below). The thicker the paper, the worse the shingling. The excess paper is trimmed by the printer.
At this point, if you looked at the inner spreads, you would notice that the left and right outer margins had become consecutively narrower toward the center because the paper was trimmed. This narrowing of the margin, or the apparent movement of the page contents toward the edges, is called "creep".
To compensate for this, special software is used to adjust the margins and page contents so that no creep is visible after trimming. This process is usually applied by the printer, so Mac Artists don't normally have to worry about it. However, there's a lesson here for designers: avoid using tight margins when designing a saddle-stitched book on heavy stock.
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