Many of our products offer a vertical or horizontal perforation option. If you've clicked on this "learn more" button, than more than likely the product you're in the middle of ordering offers this option. The vertical or horizontal perforation option is basically a straight line perforation designed for pieces that require an easy manual tear-off of a rectangular portion of the printed product.
For example, you've ordered a tri-fold brochure and one of the panels (left or right) of the brochure need to be perforated as it is meant to be separated and used as a Business Reply Card (BRC). A perforation will make it easy to cleanly tear it off and mail it. It could also be a coupon, sample swatch, etc. or anything that was meant to be separated from the larger printed piece with ease.