The easiest way to understand a bleed is to think of it as the portion of the image around the edge which could be cut so that the image touches the very edge of the print.
Due to the analog cutting process which happens after printing, it is never an exact knowledge of where the paper will be cut and end. To guard against such issues, printers long ago created the bleed edge. Therefore, you never would put anything important (copyrights, signatures, titles, important parts of the artwork itself etc.) inside this area around the edge of your artwork, because the cut will fall somewhere within this area.
The following bleed edge requirements need to be considered when preparing any artwork for printing:
- Prints up to and including 8x10: 5% bleed edge per side.
- Prints larger than 8x10: 1/4th of an inch bleed edge per side.
- All non-print (merchandise) products: 5% bleed edge per side.
- Calendars: 1/4th of an inch bleed edge per side, 3/8th of an inch on the bottom.
- The bleed edge should be considered to exist inside the image itself. If you wish to add a border to your image, that is acceptable, but not required. However, added borders should look aesthetic and suitable to the artwork, in terms of thickness and color.