When any image or element on a page touches the edge of the page, extending beyond the trim edge, leaving no margin it is said to bleed. It may bleed or extend off one or more sides. Photos, rules, clip art, and decorative text elements can bleed off the page.
Elements that bleed off the page can sometimes add to the cost of printing if the printer must use a larger size of paper to accommodate the bleed allowance. To reduce costs, if possible redesign to eliminate the bleed or reduce the page size enough to fit the work on a smaller parent sheet of paper.
A bleed is usually an intentional design element; however, sometimes an unintentional bleed can occur when the page is trimmed too much. This can happen with margins that are not wide enough.
For tutorials on setting bleeds in desktop publishing software, see Bleed Allowance.