A correctly-designed bleed or full bleed layout means the image or background color will print all the way to the edge of the page without leaving a white margin.
Here's an example of a full-bleed layout with the image touching the page edge/bleed edge.
- This was designed in BookWright so the bleed edge is the outer edge of the pink shaded area.
- The red dotted line is the estimated trim line.
- Regardless of the program you use to make your book, bleeds must be designed beyond the trim line and reach the page edge/bleed edge.
Below is a close-up of the bleed. Notice how the image runs past the red dotted trim line and all the way to the page edge.
If the bleed was designed incorrectly it might look like the example below, with a margin (white line) visible since the image doesn't run all the way to the edge:
A printed book with incorrectly-designed bleeds might look something like this, with a thin (and unwanted) white edge. The trim line is only an estimate so bleeds must go past the trim line and all the way to the page edge to avoid this problem. You might want to read up on designing bleeds in our different creation tools.