Monsignor is a form of address or title for certain members of the clergy in the Catholic Church. Monsignor is the apocopic form of the Italian monsignore, meaning "my lord". "Monsignor" can be abbreviated as Mons. or Msgr. From Wikipedia
Following his death, the Vatican confirms the late pontiff's wish for a modest tomb outside St. Peter’s Basilica, reflecting his humility and Marian devotion.