Definitions - Abbreviations - Literature references

Definitions

For the most recent discussion about definitions, see also the proposal for the New classification system

Joint issues (emissions conjointes - Gemeinschaftsausgaben / Freundschaftsausgaben) are stamps released by two or more countries on the occasion of a common event or anniversary and that are characterized either by a common design or the same date of issue. Cases where the issue date is the same but the design different, are refered to as parallel joint issues (emission parallèle). On the contrary, when the design is identical, but the lag in issuing the stamps is greater than 3 days the issue is termed a concerted joint issue (emission concertée). In case of doubt, the proof that both postal administrations intended to work together must be provided (e.g. same design but difference in date of issue too large, or, almost same date, same event, but different design and no mention on the stamps about the cooperation)

Twin issues (emissions jumelees - Zwillingsausgaben) are special cases of joint issues where design and issue date are identical for all the countries involved. 

When a large number of stamps are issued by a large number of countries (omnibus twin or joint series), those are taken in account only if these stamps are provided by different stamp printers (e.g. Europa CEPT or Norden twin issues are taken in account, but not Commonwealth small countries or islands omnibus series)

Se-tenant joint issues (emissions conjointes se-tenant - Se-tenant Gemeinschaftsausgaben) replacing the previously named Siamese issues are a special case of twin issues where the stamps of the two issuing countries are printed se-tenant. In extreme cases we have unique issues (emissions uniques - Einzelausgaben) for which only a single stamp bearing the names of all the countries involved is printed, a case which is very seldom.
 

When issuing countries are only dependencies or colonies of the main issuing country, issues cannot be considered as true joint issues and are therefore identified as territorial or colonial joint or twin issues (emissions conjointes territoriales ou coloniales - lokale oder koloniale Gemeinschaftsausgaben). Territorial or colonial joint issues can of course be parallel or concerted issues.

When the event is common, but design and issuing date are different, the issue is termed a common issues (emissions communes - gemeinsame Ausgaben). These stamps are usually not reported because they are out of the scope of the studies and the catalogue (absence of cooperation between postal administrations).
 

Sometimes stamps from one country appear to announce a joint issue from another country but in reality this second stamp is never released. This would be a unilateral issues (emissions unilaterales - einseitige Ausgabe). Normally these stamps are not listed here, except in some rare cases when a stamp was under preparation but was never issued for political or technical reasons (aborted joint issue - emission conjointe avortee - gescheiterte Gemeinschaftsausgabe).

Abbreviations
 

Literature references 
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