It's the little row of tiny holes that are between the stamps, making it easier to separate them.
Mis-perforations are a highly collectible item. Depending on how severe the perforation shift is, it could be worth a few hundred dollars. Your best bet would be to consult a dealer in your area. Probably the most could be obtained by having it in a well advertised philatelic auction.
It is a hole
HARDING MEMORIAL ISSUE 1923 Denomination: 2c Color: Black Print Method: Rotary Perforation: 11 (horizontal) VALUE: Used $25,000.00
Perforation means that there is a hole of some size in some organ ~ See related link below to several examples as to how the word "Perforation" is applied to a medical setting .
Start by buying the Scott Catalogue for use in referencing. Read about stamps on your computer, join a sstamp club. Every collector is different and both used and unused stamps have places in our collections. This becomes especially true when the mint copy of a stamp is priced beyond our means. A collector will then "settle" for a used copy, or if the stamp is extremely expensive and even the used copy is too costly, a collector will settle for a stamp with a Fault (missing piece, tear, clipped perforation, hole, scuff, thin spot, crease, toning, oxidation, stain, short perforation, etc. on a stamp). Value for a stamp is based on its "rarity" as well as its condition. There are some stamps worth more used than mint. It is not impossible to collect almost every US stamp issued since 1924 in mint very fine, never hinged condition. (This would be the top condition of a stamp). Welcome to the world of Stamp Collecting.
{| |- | This time frame is one of the biggest challenges for a US stamp collector. During this time there were many different versions of printings and perforation types. Minor color variations can make a big difference in value as well. You'll have to do some serious research to determine exactly which stamp and its value. Consult a stamp catalog such as Scott's, for a description on how stamps are rated and graded. |}
The purpose of perforation depending on what one is talking about. In the case of oil well, the purpose of perforation is to allow the oil or gas to flow more easily to the wellbore to get it out of the ground.
To perforate paper effectively, use a perforation tool like a rotary perforator or a perforation blade. Place the paper on a flat surface and run the tool along the desired line of perforation with steady pressure. This will create clean and precise perforations on the paper.
The misprinted 13-cent Liberty Bell stamp features a notable error where the perforation runs directly through the middle of the bell, creating two distinct halves. This kind of printing mistake is highly sought after by collectors, as it adds uniqueness and rarity to the stamp. Such misprints can significantly increase the stamp's value, depending on its condition and demand among philatelists. Collectors often view these errors as fascinating pieces of postal history.
540.0
531.90
Open-hole completions DO NOT include perforation because the casing in this kind of completion is drilled to the top of the oil reservoir and is not sealed at the bottom. The completion that includes perforation is cased-hole because the case must be inserted to the hydrocarbon supply. The perforations then allow the minerals to enter the wellstream.