Ecclesial ministers
Some persons within the church are called by God and the assembly to serve as ministers to the whole people of God. These people respond to this vocation by receiving the proper formation, usually including graduate studies in theology or divinity, and then exercising some leadership role in the community. In common usage, when someone refers to a "minister of the church" they are referring to any one of these "professional" ministers.
The Catholic Church identifies five ecclesial vocations, three of which are ordained. Theologians and lay ecclesial ministers are not necessarily ordained, while bishops, presbyters, and deacons are ordained. While only the later are considered clergy by the Catholic Church, all are considered ministers in the professional and vocational sense.
Read more about this topic: Minister (Catholic Church)