Clergy Titles
Here's a quick description of the subset classes that clergy members can have:
Abbot
Members of the clergy who have been granted an Abbey to run are called Abbots. Anyone can be an Abbot, even secular lords, though it is more likely to be run by a member of the clergy, and even more likely that a Master of an Order of Friars will be granted an Abbey. His form of address is "the Right Reverend".
Cleric
Members of the clergy who have a position in both the administrative wing of the government and the church are called clerics. They may be Priests, Deacons or Friars.
Chaplain
Clergy may enlist in the military in addition to their normal ecclesiastical duties. Priests and Deacons who serve in a military position by either being in a military order or joining a secular army for a campaign are called chaplains.
Master of the Order
When members of the church form a spiritual order, they may elect from among their members a "leader" or the Bishop may found an order and assign someone to lead it. This person then becomes the Master of the Order. The Master may be a Priest, Deacon or a Friar when the order is founded, but must be ordained as the founding requirements of any spiritual order would require such. They are titled “the Very Reverend”
Parson
Parsons are members of the clergy who serve as the head of a church building. This person answers only to the Bishop. They may only be a Priest and are styled "the Reverend Father".
Prior
Members of the clergy who have been granted a priory to run OR members who have been assigned by an Abbot to help them run their Abbey. They may be friars, deacons, or priests. Addressed as "the Very Reverend".
Rector
Members of the clergy assigned to teach deacons. They may only be priests and are styled "the Very Reverend Father”.
Vicar
Vicars are members of the kingdom who serves as the second in command to the Bishop. There is only one per diocese, and he/she answers only to the Bishop. They may only be a priest and are styled "the Very Reverend ".