Philately has many collectibles. Stamps are obvious; covers are stamps on envelopes and are derivative from the stamps themselves. And Proofs and Essays are precursors, coming before (and sometimes instead of) the stamps that they are associated with. As all of these types of philatelic material are related to the official issuance and use of stamps, they have always been esteemed by collectors. But what about Printer's Waste?
Printer’s Waste is a fairly amorphous term. Technically it means any printing related to postage stamps done by stamp printers that was not turned over to the postal agency that contracted for the printing and which has somehow found its way into philatelic hands. Sometimes the stamps have been sold to collectors by the printers themselves; sometimes they have been thrown away as trash (and reclaimed by trash pickers), and sometimes they were stolen from the printers or the printer’s archives to be sold to collectors. Printer's Waste can be fully printed postage stamps differing only in being imperfect or in a different color than the issued color or having some other distinguishing characteristic from the issued stamp. Or Printer's Waste can even be as rough as partial stamp designs printed on paper that was used to clean or season the plates.
Printer's Waste is popular in some countries, such as France, and has always been considered part of the mainstream collecting experience. In other areas, such as many Latin American countries, Printer's Waste on some issues seemed to be created for collectors, with many unusual and imaginative errors being created. The stamps illustrated above are from the early issues of France. French Printer's Waste is not scarce, though collectors must have been hoarding it for over the last twenty or thirty years. When I was young in this hobby, you would see it quite often in specialized France collections. Now, it is seen less often and it sells for decent prices.