An auxiliary bishop (also called vicar bishop, suffragan bishop, or chorepiscopus) is a bishop with no territorial authority working under the authority of a diocesan bishop. The auxiliary typically is given episcopal functions to assist the work of the diocesan hierarch under whose authority he operates. He typically holds the title of a city within the diocese of his superior or sometimes that of an ancient and extinct episcopal see, though in neither case is he considered the ruling bishop in that city.
In the ancient Church, the chorepiscopus (sometimes called a "country bishop") was like the modern auxiliary bishop but usually served in the countryside near a city which had its own bishop and under whose authority he operated. He did not typically have authority to perform ordinations but could function in other episcopal ways. It is generally believed that the chorepiscopate developed in the part of the Roman Empire which is modern day Romania.