Registration
How exactly the separate ink layers line up. Off by a hair and edges get colored halos, like a badly printed comic book.
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What it is
Full-color printing lays down one ink at a time: cyan, magenta, yellow, black, plus any spot inks. Registration is how precisely those separate passes land on top of each other. In register, edges are crisp. Out of register, you get colored fringes on one side of every shape and thin white slivers on the other, because the paper stretched, the web wandered, or the plates were hung slightly off.
It matters most where two solid colors meet with no black outline, and on small reversed type, where a fraction of a millimeter turns 6pt white text into a blurry mess. Prepress fixes it in the file with trapping: a tiny deliberate overlap (roughly 0.1 to 0.2mm) so a shift never opens a gap. Press operators fix it on the machine by watching the registration marks and nudging the plates.
Worth knowing: bad registration is sometimes the whole point. Risograph, screen-printed gig posters, and old comic books wear their misalignment as style, and 'offset the layers by a couple of millimeters' is a real design instruction. Two practical rules: multi-color small text is asking for trouble (set it in one ink), and the more inks a design stacks along one edge, the more registration error it will show.
Ask AI for it
Recreate a misregistered print look: split the artwork into flat cyan, magenta, and yellow layers set to multiply, then nudge each layer 2 to 4px in a different direction so edges fringe and thin paper-white gaps open where shapes meet. Add slight ink texture and a soft edge on each layer, keep the type in a single ink so it stays readable, and aim for the look of a Risograph or a 1970s comic rather than a clean modern offset print.