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A page bleed is a technique used to compensate for, or eliminate, mechanical problems when your project is being trimmed after printing. If the graphic element such as pictures, graphics, or background color is not carried beyond the edge of the page, there is the possibility that a small area of blank page will be seen at the edge after the page is trimmed.
When page elements, such as pictures, graphics or background, touch the document-page edge, they will need to be extended beyond the page. The amount to extend is called a page bleed. Typically a bleed will extend 1/8 in. (3.175mm or 9 points) beyond the edge of the page. Some professional page-layout programs allow for a value to be entered in the document setup. This page-bleed option allows the artist to specify which edge(s) of the page will require bleeds and at what measurement.
Adobe® InDesign® allows you to enter a Bleed amount when creating a New Document. You may have to click the More Options button on the menu to display the bleed options.