Monsignor, pl. monsignori, is the form of address for those members of the clergy of the Catholic Church holding certain ecclesiastical honorific titles. Monsignor is the apocopic form of the Italian monsignore, from the French mon seigneur, meaning "my lord". It is abbreviated Mgr, Msgr, or Mons.
As a form of address, "Monsignor" is not itself an appointment (properly speaking, one cannot be "made a monsignor" nor can one be "the monsignor of a parish"). The three awards or offices most often associated with the style "monsignor" are Protonotary Apostolic, Honorary Prelate, and Chaplain of His Holiness. These awards are granted by the Pope, usually at the request of the local bishop.
Read more about Monsignor: Title and Forms of Address, Classes of Monsignori, Ecclesiastical Dress, Other Monsignori