USPS stamps are made up of three different types of stamps: adhesive stamps, imperforate stamps, and stamps with perforations. Adhesive stamps are the most common type of stamp, and are made from a paper backing that adheres to the front of the stamp to create the image of the stamp. Imperforate stamps are made from a single sheet of paper that is perforated all the way through, so that the stamps can be separated into individual stamps.
Stamps with perforations are similar to imperforate stamps, but the perforations are not evenly spaced. Instead, they are spaced in a pattern, so that the individual stamps can be separated.