A deanery is the territorial jurisdiction of a dean.
"Parishes of a diocese are usually gathered into deaneries in order to promote joint pastoral action and the best possible distribution of ministry, and to provide for the pastoral care of the priests serving in each area of the diocese" (La Crosse).
"The care of the deanery is confided by the diocesan bishop, after consultation with the priests of the deanery, to one of the priests ministering in the deanery" (La Crosse). This individual is called the dean.
In a practical way, the main roles of the dean are to help support the deanery clergy: To provide information between the deanery parishes and its diocese. The dean may also help with parish matters and, in some cases, represent the bishop.
They may also coordinate endeavors within the deanery, including services, fund raisers, and other activities.