True
Non-terrain chords are specifically just 3rds stacked on top of each other
The Mass ordinary, or the Ordinarium parts of the Mass, is the set of texts of the Roman Rite Mass that are generally invariable. ... The Kyrie, Sanctus, and Agnus Dei are part of every Mass. Kyrie, Gloria, Credo, Sanctus and Agnus are often sung, by a choir if not by the whole congregation.