The word “ministry” can be equated to mean the work that the church does in the world. Therefore anyone who does “ministry” is a minister. This includes priests, deacons, women religious, brothers and lay professionals (like youth ministers and campus ministers).
Usually all of these people hold a master’s degree in theology, divinity, pastoral ministry or religious education. Some are ordained or have made promises or vows to a religious community, while others are not and are merely employed by a particular parish or diocese or religious community.
Taking my own parish as an example we have an ordained priest who serves as the pastor, a religious sister who is the pastoral associate, 3 lay people who are the director of religious ed, the youth minister and the campus minister. We also employ a deacon part time to be a marriage and baptism minister. All of us are ministers together but only two (the priest and deacon are ordained).