Bleed is a printing term that refers to printing that goes beyond the edge of the sheet before trimming. In other words, the bleed is the area to be trimmed off. The bleed is the part on the side of a document that gives the printer a small amount of space to account for movement of the paper, and design inconsistencies. Artwork and background colors can extend into the bleed area. After trimming, the bleed ensures that no unprinted edges occur in the final trimmed document.
It is very difficult to print exactly to the edge of a sheet of paper/card so, to achieve this, it is necessary to print a slightly larger area than is needed and then trim the paper/card down to the required finished size. Images, background images and fills which are intended to extend to the edge of the page must be extended beyond the trim line to give a bleed.
Please view the bleed tutorial below.