A diocese is the area that a bishop oversees in certain Christian churches, particularly the Catholic, Eastern Orthodox, and Anglican churches. Think of it like a district or territory: just as a principal manages one school, a bishop leads all the churches and parishes within their diocese.

A diocese might cover a city, several counties, or even an entire state, depending on how many Christians live there. For example, the Diocese of Los Angeles covers several counties in Southern California, while the Diocese of Cheyenne covers the entire state of Wyoming.

Each diocese contains many individual churches grouped into local communities called parishes, and the bishop's main church is called a cathedral. The bishop coordinates the work of all the priests in the diocese, confirms young people in their faith, and serves as the spiritual leader for the entire region.

The person who leads a diocese is called a bishop or sometimes a diocesan bishop. In the Catholic Church, some bishops report to archbishops, who lead larger regions called archdioceses.