Preprinted labels as collected by philatelists come in three broad categories: postage stamps, revenues, and Cinderellas. Postage stamps are collected by all philatelists. They are the major stamp issues of each country and are issued for the prepayment of postage. Postage Stamps are listed in many major worldwide catalogs. Collecting postage stamps has a long history and is very popular. Revenues are stamps that are issued to pay taxes, not postage. However, some countries allow the use of some stamps for both purposes; when this happens, the stamps are called Postal Fiscals and are collected by stamp collectors either mint or with postal, not revenue, cancels. Revenue collecting was once very popular and rivaled postage stamp collecting. It is very much of a niche area of the hobby now. Outside of the US philatelic domain, collecting of Revenue stamps is very unusual.
Cinderellas have always been the poor sister of philately (hence the name for these types of stamps