The ordinary, in Roman Catholic and other Western Christian liturgies, refers to the part of the Eucharist or of the canonical hours that is reasonably constant without regard to the date on which the service is performed. It is contrasted to the proper, which is that part of these liturgies that varies according to the date, either representing an observance within the liturgical year, or of a particular saint or significant event, and to the common, which contains those parts that are common to an entire category of saints, such as apostles or martyrs.

The ordinary of both the Eucharist and the canonical hours does, however, admit minor variations in accordance with the seasons, such as omission of “Alleluia” in Lent and its addition in Eastertide.

These two are the only liturgical celebrations in which a distinction is made between an ordinary and other parts. It is not made in other celebrations of Christian liturgy: administration of sacraments other than the Eucharist, blessings, and other rites.

In connection with liturgy, the term “ordinary” may also refer to Ordinary Time – those parts of the liturgical year that are part neither of the Easter cycle of celebrations (Lent and Eastertide) nor of the Christmas cycle (Advent and Christmastide), periods that were once known as “season after Epiphany” and “season after Pentecost”.

In addition the term “ordinary liturgy” is used to refer to regular celebrations of Christian liturgy, excluding exceptional celebrations.

https://en.wikipedia.org/wiki/Ordinary_(liturgy)

Dies irae (Latin pronunciation: [ˈdi.ɛs ˈi.rɛ]; “Day of Wrath”) is a Latin sequence attributed to either Thomas of Celano of the Franciscans (1200 – c. 1265)or to Latino Malabranca Orsini (d. 1294), lector at the Dominican studium at Santa Sabina, the forerunner of the Pontifical University of Saint Thomas Aquinas, Angelicum in Rome.^[2] The sequence dates from at least the thirteenth century, though it is possible that it is much older, with some sources ascribing its origin to St. Gregory the Great (d. 604), Bernard of Clairvaux (1090–1153), or Bonaventure (1221–1274).

It is a Medieval Latin poem characterized by its accentual stress and rhymed lines. The metre is trochaic. The poem describes the Last Judgment, trumpet summoning souls before the throne of God, where the saved will be delivered and the unsaved cast into eternal flames.

It is best known from its use in the Requiem (Mass for the Dead or Funeral Mass). An English version is found in various Anglican Communion service books. The melody is one of the most quoted in musical literature, appearing in the works of many composers.

Source: Dies irae – Wikipedia