Rightly so called; strictly considered; as, Greece proper; the garden proper.
chants and prayers of the Mass that change daily, throughout the church year. The changes occur according to the liturgal occasion. The musical sections of the Proper consist of the Introit, Gradual, Alleluia, Offertory, and Communion. The term is strictly used to define Mass chants. [GRD
a liturgical genre is proper if its text changes from one day to the next. In the mass, the musical items of the proper are the introit, gradual, alleluia, offertory, and communion. A table of items from the mass is available.