You’ve probably noticed that your home printer leaves a small white border around the edge of the paper: this simply wouldn’t do for professionally printed products.
To solve this issue we add bleed to the edges of the page. This is usually 3mm from the edge of the artwork. Cutting isn’t 100% accurate so a bleed area means that you don’t get an unwanted border leftover after the job is cut.
When extending your artwork to fill the bleed area you should use either the background image or the background colour.