What is a Diocese

A diocese is the territorial jurisdiction of a diocesan bishop. The term also refers to the congregations and church members of the diocese. Before the church adopted the word it had a long secular usage. It was originally used in the Roman Empire for an administrative subdivision. A diocese was a division of a prefecture of the Roman Empire. In the reorganization of Diocletian and Constantine, the Roman Empire was divided into twelve dioceses. As the church expanded out from the cities, it adopted the use of the word “diocese,” and ecclesiastical dioceses tended to correspond to civil units.

Every diocese in the Episcopal Church has a Standing Committee. When there is a bishop in charge of the diocese, the Standing Committee is the bishop's council of advice. When there is no bishop, bishop coadjutor or suffragan bishop, the Standing Committee is the ecclesiastical authority of the diocese. A diocese usually meets annually in a diocesan convention. Each diocese is entitled to representation in the House of Deputies by not more than four ordained persons, presbyters or deacons, canonically resident in the diocese, and not more than four lay persons, who are confirmed adult communicants of the Episcopal Church and in good standing in the diocese. Dioceses also elect clerical and lay deputies to the Provincial Synod. The Constitution and Canons of the Episcopal Church provide guidelines for the division of a diocese. Some persons insist that the diocese is the primary unit in the Episcopal Church.

https://www.episcopalchurch.org/glossary/diocese/