Counterfoil

A counterfoil is part of stamp used as a control. It is included with the stamp as an attached tab. This can be attached to the bottom of a stamp or to its side. When used, the counterfoil is detached and taken by a clerk or mail carrier.

Italian and Italian area parcel post stamps are an example of this. Italian parcel post stamps were/are used on postal forms, typically cards, with one or both parts cancelled and one part left attached to the form. A fair number of revenues from different countries use this feature also with the main part attached and cancelled on a document or form. In the latter, both revenue and counterfoil might be numbered.

In practice, this is a good idea for receipting and control, but the execution was poor often enough. Either half could be left on a document and the stamp instead of the counterfoil would be taken away. In other cases, both stamp and counterfoil would be left on the document. The latter happened often enough that collectors favor complete used stamps with counterfoils. 

