Titular bishop

A titular bishop in various churches is a bishop who is not in charge of a diocese.
By definition, a bishop is an "overseer" of a community of the faithful, so when a priest is ordained a bishop, the tradition of the Roman Catholic and Orthodox churches is that he be ordained for a specific place. There are more bishops than there are functioning dioceses. Therefore, a priest appointed not to head a diocese as its diocesan bishop but to be an auxiliary bishop, a papal diplomat, or an official of the Roman Curia is appointed to a titular see.

Eastern Orthodox Church

Titular bishops and titular metropolitans are often appointed in the Eastern Orthodox Church. In Ecumenical Patriarchate of Constantinople, titular bishops and metropolitans are usually appointed with titles of former dioceses in the regions of Thrace, Asia Minor and Pontus (now Turkey), that were often active until the Greek-Turkish population exchange of 1923. In Serbian Orthodox Church, titular bishops are usually appointed to serve as auxiliary bishops, assisting diocesan bishops in various fields of diocesan administration.