WHAT ARE IMPERFORATED STAMPS?
Stamps with no perfins at any side, nor rouletted.
Imperforated stamps are popularly known as "imperfs". The earliest stamps were all imperforate. Likewise, many later self-adhesive stamps are imperforate. Today most imperfs are part of a larger production line, but with the normal perforation excluded. Not many modern stamps are issued only as imperforated even as self-adhesive stamps are gaining popularity. Some imperfs are referred to as errors, where the perforation tools failed to perforate the paper sheet. Other imperfs can be proofs where no perforation was required to examine the print.
Imperforated stamps have become a popular field of collecting stamps, as a sole category of interest, or as a compliment to perforated stamps; a way to "add specialization" to a collection of "normal" stamps with complimentary imperforated stamps, or to build a collection solely with imperforated stamps organized by country or topics.