Score / perforation
A score is a pressed crease so thick paper folds without cracking; a perforation is a dotted line of tiny cuts so a piece tears off clean.
See it
What it is
Two finishing operations that both put a line in the sheet, for opposite reasons. A score presses a channel into the paper so the fibers bend instead of snapping, which is the difference between a crisp fold and a cracked, flaking spine on anything above roughly 170gsm. A perforation cuts a dashed row of tiny holes so a human can tear the piece cleanly by hand: raffle tickets, coupons, remittance stubs, tear-off flyer tabs.
Reach for a score on every folded card, brochure, or box panel printed on cardstock, and on any fold that crosses heavy ink coverage (ink makes the surface more brittle, so it cracks first). Reach for a perf whenever part of the piece is supposed to leave with someone. Perf strength is tunable, but teeth per inch on its own tells you almost nothing. What decides the tear is the cut-to-tie ratio (how much of the line is slit versus how much paper is left holding), the tooth geometry of the rule, and the stock. Describe the behavior you want, a clean easy tear or a stub that survives the mail, and let the printer pick the rule.
Gotcha: scoring is not folding. You still specify which way the panel folds, because a score bends best away from the pressed side, and folding against the paper's grain direction cracks even when scored. Mark scores and perfs on separate technical spot-color layers using the printer's own line-style legend, never as visible printed dashes, or you get a printed dotted line and no actual tear. Setting those lines to overprint does not make them nonprinting either: they have to be flagged nonprinting or held out of the output separations the way the vendor specifies.
Ask AI for it
Draw a print production layout for a folded card with a tear-off portion. Put all artwork on one layer, then put the crease and the tear line on separate technical layers named the way the printer asks, drawn as 0.25pt strokes in vendor-named technical spot colors following their line-style legend. Mark those layers nonprinting or exclude their separations at export exactly as the vendor specifies, because overprint does not stop a line printing. Label each line 'SCORE' or 'PERF' outside the trim edge, keep live text at least 5mm clear of every crease and perf, show the fold direction with a small arrow, and state the tear behavior you want so the printer can choose the perforation rule.