The definition of a supply pastor varies some from denomination to denomination. I happen to work as a supply pastor for the Cumberland Presbyterian Church and am an installed Associate Pastor of Education and Outreach in a part-time position. Since my position as Associate Pastor of Education and Outreach is part-time, I have the opportunity to help out other church on Sunday mornings when my services are not required at Lebanon. This allows me to preach periodically in other churches.
A supply pastor is a person that has preaching credentials, or is working on his/her preaching credentials and is able to work as a ‘substitute pastor’ for a short time. In some cases they are retired ministers that still have a desire to preach when they are able and needed. Sometimes it is a pastor that is between churches. Churches that need a pastor for a Sunday, or two will hire a supply pastor to preach for the worship services and perform any other ministerial services that the church requests.
The advantage of supply pastors is that churches can allow their pastor to have time off periodically and not have to be concerned the spiritual leadership of the church. This is especially true for the small country churches that have only one pastor. Sometimes when churches are looking for pastors but don’t have a pastor for a given week, they may ask a supply pastor to come for that week.