The bleed is the margin extending beyond the final format of the print product and will be trimmed by the cutting machine. Print-ready artwork refers to the finished size of your printed product including the bleed. Without bleed, you can have a white border margin around the trim edge. To prevent this, any elements that will print to the edge of the finished product should be extended beyond this edge out to the bleed edge.
If not specified otherwise, add 0.1 inch of circumferential bleed to your print files. The bleed should not be colorless but have the same color as the design at the final trim edge. For example, (background) elements at the edge of your design should extend into the bleed zone. But make sure that no critical content extends beyond the final trim size because it might be cut off.
Why is the bleed necessary?
When cutting to final format, there can be deviations by up to 0.04 inch.
The bleed thus serves as tolerance for possible trimming differences.
Safety margin for important design elements
Position critical graphic and text elements at least 0.2 inch away from the final trim size unless otherwise specified.
If you include the bleed, these elements should hence keep a distance of at least 0.24 inch from the edge of the print file.
Please bear in mind that wire-O bound products such as catalogs may require bigger safety margins.
For more information, see the data sheet of the product in question.
MARKERS & REFERENCE LINES
Feel free to use appropriate markers and reference lines (e.g. cutting, folding or register marks) to design your product in your layout software. However, these must not be included in the export of the print files.
If this is impossible for program reasons, only include cut marks when creating print files.