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A postal administrations may allow a thrid-party agency to issue stamps on its behalf. When the vast majority of issued stamps are sold directly by the agency to the philatelic market rather than used in the postal system, we mark them as "Agency Issue". They are rarely found on everyday mail.

Airmail (or air mail) is a mail transport service branded and sold on the basis of being airborne. Airmail items typically arrive more quickly than surface mail, and usually cost more to send. Airmail may be the only option for sending mail to some destinations, such as overseas, if the mail cannot wait the time it would take to arrive by ship, sometimes weeks. The Universal Postal Union adopted comprehensive rules for airmail at its 1929 Postal Union Congress in London. Since the official language of the Universal Postal Union is French, airmail items world-wide are often marked Par avion , literally: "by airplane".

These stamps are intended for mail that will be transported by air. Some either include or are solely for the payment of an additional air post fee and are required for air post transportation. Others just have the correct value for air post, but can also be used for other types of postage.

These are Official stamps that are also Air Post stamps.

These are Semi Postal stamps that are also Air Post stamps.

A variable value stamp, is a gummed or self-adhesive postage stamp of a common design, issued by a machine similar to an Automatic Teller Machine, with a value of the user's choice printed at the time the stamp is dispensed. The value may be variable or from a fixed selection of postal rates. The stamps and machines are typically for use in retail or post office environments. As only the postal value varies from stamp to stamp, these stamps have been described as key type stamps. They are also closely related to meter stamps from postage meters.

A “cinderella stamp” is anything that looks like a stamp but is not an actual postage stamp (that is to say they are not stamps that were issued by a governmental authority of a country to be used to pay for postage). Cinderella stamps include:

• Stamps that have been produced under the governmental authority of a country but not for postal usage, such as charity stamps, and various kind's of tax stamps (these tax stamps are known as “Revenues” and listed as a separate emission type on Colnect).
• Stamps that are used to pay for postage (delivery) but have been produced under the governmental authority of a place that is not a “country”, such as stamps by a government in exile, or stamps from a territory or a micronation that was never recognized by the United Nations, the UPU, or its neighbors.
• Legitimate stamps that are used to pay for postage (delivery) but that have not been authorized by the government, such as stamps for use by private courier companies. These private delivery cinderella stamps are listed as stamps with the emission type “Private” on Colnect.
• Stamp shaped seals and labels that are produced in a place that is a country but that have not been authorized by its government and are not used to pay for postage or delivery, such as Christmas seals, propaganda stamps, and various other charity seals and labels.
• Stamps that are fakes or forgeries of genuine postage stamps produced in order to deceive postal administrations and/or collectors.
• Stamp shaped seals that have a fictitious country name or no country name at all that were printed to sell to collectors.
• And anything else that looks like a stamp but is not an actual postage stamp.

A commemorative stamp is a postage stamp, often issued on a significant date such as an anniversary, to honor or commemorate a place, event, person, or object. The subject of the commemorative stamp is usually spelled out in print, unlike definitive stamps which normally depict the subject along with the denomination and country name only. Many postal services issue several commemorative stamps each year, sometimes holding first day of issue ceremonies at locations connected with the subjects. Commemorative stamps can be used alongside ordinary stamps. Unlike definitive stamps that are often reprinted and sold over a prolonged period of time for general usage, commemorative stamps are usually printed in limited quantities and sold for a much shorter period of time, usually until supplies run out.

A definitive stamp is a postage stamp that is part of the regular issue of a country's stamps, available for sale by the post office for an extended period of time and designed to serve the everyday postal needs of the country. The term is used in contrast to a "provisional stamp", one that is issued for a temporary period until regular stamps are available, or a "commemorative stamp", a stamp "issued to honor a person or mark a special event" available only for a limited time. Commonly, a definitive issue or series includes stamps in a range of denominations sufficient to cover current postal rates. An "issue" generally means a set that is put on sale all at the same time, while a "series" is spread out over several years, but the terms are not precise. Additional stamps in a series may be produced as needed by changes in postal rates but some values may be permanently available, regardless of prevailing rates, for instance 1c or 1p and £1 or $1.

Express is a postal service paid for with additional postage for urgent letters and postal packets which are delivered in less time than by standard or first class mail service. Its meaning is different and separate from express mail delivery service. Essentially it means that a postal packet is delivered from a post office to the addressee immediately once it arrives at the post office responsible for delivering it, rather than waiting for the next regular delivery to the addressee.