An Ambassador is an official envoy; especially, a highest ranking diplomat who represents a State and is usually accredited to another sovereign State (country), or to an international organization as the resident representative of his or her own government or sovereign or appointed for a special and often temporary diplomatic assignment. The word is also often used more liberally for persons who are known, without national appointment, to represent certain professions, activities and fields of endeavor.
In its most common use, the term usually applies to the ranking government representative stationed in a foreign capital. The host country typically allows the ambassador control of specific territory called an embassy, whose territory, staff, and even vehicles are generally afforded diplomatic immunity in the host country.
The equivalent to an Ambassador exchanged among members of the Commonwealth of Nations are known as High Commissioners. The "Ambassadors" of the Holy See are known as Papal or Apostolic Nuncios.
As formally defined and recognized at the Congress of Vienna (1815), ambassadors were originally regarded as personal representatives of their country's chief executive rather than of the whole country, and their rank entitled them to meet personally with the head of state of the host country. Since 1945 all nations have been recognized as equals, and ambassadors or their equivalents are sent to all countries with which diplomatic relations are maintained. Before the development of modern communications, ambassadors were entrusted with extensive powers; they have since been reduced to spokespeople for their foreign offices.
The term is derived from Middle English badassadour, Anglo-French ambassateur, ultimately of Germanic origin; akin to Old High German ambaht service. The first known usage of the term is known to be 14th century.