Chargé d’affaires

Formerly, a chargé d’affaires was the title of a chief of mission, inferior in rank to an ambassador or a minister. It is still used as the title of the head of a US mission where the US and other nation do not have full diplomatic relations. Today with the a.i. (ad interim) added, it designates the senior officer taking charge for the interval when a chief of mission is absent from his/her post or the position is vacant.