The title of "Monsignor" is a title of distinction given by the Pope to certain priests in the Roman Catholic Church as part of a papal honor recognizing the priest's service to the Church. The diocesan bishop nominates candidates for the honor and submits the names, biographies etc., to the Holy See. The Holy Father then, if he wishes, confers the honor onto the priest. Once decided by the Pope, the Vatican Secretariat of State issues a diploma designating the new title and rank and recognizing the newly-made monsignor's service to the Church.
Historically, the monsignorate dates from the 14th century when the papal court operated for a period of time in Avignon, France. At that time, bishops were referred to as "mon seigneur," French for "my lord." Priests who worked in the papal curia, the administrative and judicial offices of the pope, were also referred to as "monsignor" and were allowed to wear some of the regalia of a bishop.
Today, there are generally three grades of papal honors that bear the title "Monsignor" - the Protonotary Apostolic, the Prelates of Honor to His Holiness, and the Chaplains to His Holiness. Priests who are monsignors of one rank may be elevated from one rank to another at the will of the Pope.
The Protonotary Apostolic is conferred predominantly on priests who serve on seven specific positions in the Roman Curia. These are referred to as Portonotaries of Number. Aside from these seven, the honor of Protonotary Apostolic can also be conferred on priests outside of the Roman Curia. These are called Protonotaries Apostolic Supernumerary. A Protonotary Apostolic wears a black cassock with red buttons and piping along with a fuchsia sash. A fuchsia cape can also be worn on special occasions.
The second grade of monsignor is the Prelate of Honor to His Holiness. This grade was historically associated with the chamberlain of the papal court and today can also be conferred to priests outside of the papal court. A Prelate of Honor to His Holiness, during liturgies, wears a bishop's choir cassock, which is fuchsia in color with red buttons, piping and cuffs, and a fuchsia sash. Prelates of Honor to His Holiness may also wear a bishop's black cassock, which also has red buttons, piping and a fuchsia sash.
The third grade of monsignor is Chaplain to His Holiness. This honor can be conferred to priests inside or outside of the Roman Curia. A Chaplain to His Holiness wears a black cassock with fuchsia piping and buttons along with a fuchsia sash. This is the honor that Reverend Monsignor Domenico C. Pinti has received.
Priests who are given papal honors and thus named monsignors are considered to be members of the papal household and thus are listed in the Annuario Pontificio (the papal yearbook). In 1969, the custom of Chaplains of His Holiness (a subset of the second grade of monsignor) surrendering the title upon the death and burial of the conferring pontiff was suppressed. Today, all monsignors retain their titles upon the death and burial of a Pope.
The proper way to address the monsignor is as "Monsignor Pinti" or simply "Monsignor." On paper, the reference should be "Reverend Monsignor Domenico Pinti." Note that, as with a Priest, you should stand when he enters a room (until he invites you to sit).