Magisterium: The official Teaching office of the Church.

Mary: The central point of the theology of Mary is that she is the Mother of God. From apostolic times, tradition, the Church and the faithful have accorded to Mary the highest forms of veneration. She is celebrated in feasts throughout the year, and in devotions such as the rosary and litany and is hailed the patroness of many countries, including the United States.

Mass: The common name for the Eucharistic liturgy of the Catholic Church.
Synonyms: Eucharist, Celebration of the Liturgy, Eucharistic celebration, Sacrifice of the Mass, Lord's Supper.

Master of Ceremonies: One who assisted in the preparation of the celebration and is present during it to facilitate the movement of the entire rite.

Matrimony: The Roman, Orthodox and Old Catholic churches consider matrimony a sacrament, referred to as the Sacrament of Matrimony. This is a marriage contract between baptized persons.

Metropolitan: The archbishop of an archdiocese in a province. He has limited supervisory powers and influence over the other dioceses and bishops in the province.

Military Ordinariate (Archdiocese for the Military Services, U.S.A.): Nonterritorial diocese for American Catholics and their dependents who are in the military or affiliated with the armed forces.

Minister: From the Latin word for "servant," in the ecclesiastical sense a minister is (1) an ordained cleric or (2) one who has the authority to minister to others.

Ministers of Communion: Those who assist in the distribution of communion.

Miracles, apparitions: Generally miracle is used to refer to physical phenomena that defy natural explanation, such as medically unexplainable cures. An apparition is a supernatural manifestation of God, an angel or a saint to an individual or a group of individuals.

Mitre: A headdress worn at some liturgical functions by bishops, abbots and, in certain cases, other ecclesiastics.

Monastery: An autonomous community house of a religious order, which may or may not be a monastic order. The term is used more specifically to refer to a community house of men or women religious in which they lead a contemplative life separate from the world.

Monk - Friar: A man who belongs to one of the monastic orders in the church, such as Basilians, Benedictines, Cistercians and Carthusians.

Monsignor: An honorary ecclesiastical title granted by the Pope to some diocesan priests. In the United States, the title is given to the vicar general of a diocese. In Europe, the title is also given to bishops.

Mortification: Acts of self-discipline, including prayer, hardship, austerities and penances undertaken for the sake of progress in virtue.