Auxiliary bishop Wikipedia
An auxiliary bishop, in the Roman Catholic Church, is a bishop assigned to assist the diocesan bishop in meeting the pastoral needs of the diocese. They exist in both the Latin Church and in the Eastern Catholic Churches. Auxiliary bishops are titular bishops of sees that no longer exist.
The particular duties of an auxiliary bishop are given by the diocesan bishop and can vary widely depending on the auxiliary bishop, the ordinary, and the needs of the diocese. In a larger archdiocese, they might be in assigned to serve a portion of the archdiocese (sometimes called deaneries, regions, or vicariates) or to serve a particular population such as immigrants or those of a particular heritage or language.
Canon law requires that the diocesan bishop appoint each auxiliary bishop as vicar general or episcopal vicar of the diocese.