“Bleeds” are what we call it anytime a graphic touches the edge of the material it’s applied or printed on. Depending on the specific product you are ordering, bleed margins may be required. Bleed margins are an extra little bit of graphic on the edge of a print the gets cut off. For most items that require bleed margins, an 1/8th inch on each side will do. This means that your 4″ x 6″ postcard should be set-up at 4.25″ x 6.25″.