The Church adopted the term order from its use in the roman Empire, where it referred to a governing group. In the Sacrament of Holy Orders, there are three degrees or "orders": bishop, priest, and deacon. the rite of ordination is the sacramental act that makes this possible. Ordination "confers a gift of the Holy Spirit that permits the exercise of a 'sacred power'...which can come only from
Christ himself through the Church" (CCC, no. 1538).
-- United States Catholic Catechism for Adults, p. 264.