Bleed is defined as ink going to the edge of the printed piece. If you choose to have an image on a postcard that goes edge to edge, the image bleeds on four sides. If a bar goes side to side across a letterhead, the bar bleeds on two sides. The bleed can be set up to run off the printed piece on one side, two sides, three sides or four sides. The design is limited by your imagination.
One important note before you go and set up a document with bleeds, bleeds cost extra on most printed documents. An eighth inch of image or bar or element to bleed must be added to the document. The print area of a business card that is trimmed to 2 x 3.5 inches, lays down ink in an area that is 2.25 x 3.75 inches. When the sheets dry, the cards are trimmed out to 2 x 3.5 inches and delivered.
If your software of choice does not allow you to add a bleed area to the document, you have two choices. Make sure that the images/elements extend .125 inch past the boundaries of the document. The second option is to add the extra bleed area to the document, and place guides in at the trim size. InDesign allows the user to add a bleed margin. The CS4 version of Illustrator added the document bleed feature, previous versions do not. Photoshop needs to have the bleed added to the document size. Quark users might want to consider adding the bleed to the document. Pagemaker users will also want to make this consideration. Publisher users, this is questionable, Publisher allows for a bleed. I’ve not seen a Publisher file that had bleed set correctly.
Quark and Pagemaker allows the users to print with bleeds, why would they want to add the bleed to the document? I have gotten pdf files from designers that do not have a full eighth inch bleed on all sides. I have to contact the designer/print broker and ask for more bleed. Setting up the file to have built in bleed allows the designer to use the edge of the document to make sure the file has a higher success rate on the press. If the bleed is a sixteenth inch instead of an eighth inch, the cut can be slightly off on some sheets and show white space. If you choose to add the bleed to the document, add guides for an eighth inch from the document edge and move the X/Y zero point to the eighth inch guides.