These words all denote a diplomatic representative of a head of state or of a government. An ambassador is a diplomatic officer of the highest rank, appointed as the representative of one government to another. An ambassador extraordinary is one sent on a special mission, as distinguished from one, called an ambassador ordinary, who resides permanently in the country to which he is assigned.

A minister is a diplomatic representative of lower rank than an ambassador . A minister sent on a special mission is called an envoy . Nuncio and legate are diplomatic representative of the Holy See, or Vatican State. A nuncio is an accredited ambassador of the Pope in a foreign country; a legate is a papal envoy , i.e. a diplomatic representative of the Pope dispatched to a country on a special mission.

A plenipotentiary describes any person fully empowered to represent a government, whether he be an ambassador , minister or envoy . The term is most commonly applied to minister plenipotentiary , who, though ranking below ambassadors , are nevertheless invested with full authority to conduct important matters of state in the name of their government.