The lowest of the three traditional angelic hierarchies, consisting of Principalities, Archangels, and Angels and most directly associated with divine missions toward the created world.
The Third Hierarchy contains Principalities, Archangels, and Angels. In the traditional scheme these orders are most closely associated with carrying divine messages and ministries into the created world.
Etymology
Hierarchy from Greek hierarchia, “sacred rule.”
Sculptor Notes
This hierarchy supplies many of the most familiar figurative types in Western sculpture: messenger angels, guardians, armored Michael, Gabriel at the Annunciation, and Raphael guiding Tobias.
References
https://www.newadvent.org/summa/1108.htm