Envoy Extraordinary and Minister Plenipotentiary

In diplomacy, an "Envoy Extraordinary and Minister Plenipotentiary", in short Envoy, is under the terms of the Congress of Vienna of 1815, a diplomat of the second class, ranking between an Ambassador and a Minister Resident.

Usually just referred to as a Minister, an Envoy is a diplomatic representative, not considered a representative of the head of state, but nonetheless with plenipotentiary powers (i.e. full authority to represent the government). A diplomatic mission headed by an Envoy would be called a Legation rather than an Embassy. Envoys are entitled to use the style "His/Her Excellency".

Until the mid-20th century, the majority of diplomats in the world were of the rank of Envoy, with the exchanges of ambassadors being reserved among major nations, or close allies and related monarchies. The Holy See did not use the rank of Envoy, but instead had the equivalent titles of Internuncio and (at least in Anglo-Papal diplomacy between 1914 and 1982) Apostolic Delegate.

After World War II, it was no longer considered acceptable to treat some nations as inferior to others given the United Nations doctrine of equality of sovereign states; therefore the rank of Envoy for diplomatic missions' highest-ranking officials gradually ceased. The position still existed in 1961, when the Vienna Convention on Diplomatic Relations was signed, but it did not outlive the decade. The last remaining American legations, in the Warsaw Pact countries of Bulgaria and Hungary, were upgraded to embassies in 1966.

In popular parlance, an envoy can mean a diplomat of any rank. Moreover, the rank of Envoy should not be confused with the position of Special Envoy, which is a relatively modern invention, appointed for a specific purpose rather than for bilateral diplomacy, and may be held by a person of any diplomatic rank or none (though usually held by an ambassador).

...
Wikipedia