Gregorian Chant, named after Pope Gregory I (d604), is the term applied to the vast repertoire of liturgical plainchant assembled over the course of several hundred years, roughly 700-1300 AD. There are almost 3000 extant chants in the Gregorian repertoire, with texts specific to each day of the Roman Catholic Church's liturgical year.
Rorate cæli desuper
Let dew fall from the heavens above
et nubes pluant iustum:
and let clouds rain down justice;
aperiatur terra et germinet Salvatorem.
let the earth open and bring forth a Savior.
Cæli enarrant gloriam Dei:
The heavens declare the glory of God,
Et opera manuum ejus annuntiat firmamentum Dei.
And the firmament shows forth his handiwork.
Gloria Patri, et Filio,
Glory be to the Father, and to the Son
et Spiritui Sancto.
and to the Holy Spirit.
Sicut eratin principio, et ninc et semper,
As it was in the beginning, is now,
Et in sæcula sæculorum. Amen.
And forever will be. Amen.