The bleed is a term in print that’s used to describe where elements or images touch the end of the page. Documents that have a bleed must be printed on a larger sized paper and trimmed down to the final cut line. The bleed is important because it accounts for the design inconsistencies and the movement of the paper. This small space around the final cut line gives the designer a general view of how the print version will look. It’s very difficult to print exactly at the edge of a sheet of paper so it’s easier to print a slightly larger size and then trim it down to it’s required dimensions afterwards.
The same principles apply to comic books when they are made. The innermost area of the page is the live area. This is the part where the action, characters and dialogue reside. This area is important because no matter what type of printer it is, this area will never be cut off. The trim line is where the comic will be cut off and is usually .25 in away from the live area. This is to make sure the art is cut off within the live area so that the art runs off the page. The bleed line is at least .25i n surrounding the trim line and then the edge of the bristol board is the actual document size.
Abel, Jessica, and Matt Madden. “Quickguides: Bleeds.” Drawing Words and Writing Pictures. Web.