Catechism of the Catholic Church

The word order in Roman antiquity designated an established civil body, especially a governing body. Ordinatio means incorporation into an ordo. In the Church there are established bodies which Tradition, not without a basis in Sacred Scripture, has since ancient times called taxeis (Greek) or ordines. And so the liturgy speaks of the ordo episcoporum, the ordo presbyterorum, the ordo diaconorum. Other groups also receive this name of ordo: catechumens, virgins, spouses, widows,.... (922, 923, 1631)