Holy Orders, in the Catholic Church, is the sacrament through which men are ordained as deacons, priests and bishops. It maintains the continuity of the apostles whereby each ordained person is ordained by a successor of an original apostle of Jesus Christ.
The reason it is called “orders” comes from an old Roman meaning of an established civil body, especially a governing body. Common knowledge to most Catholics the governing body of the Church is made up of the bishops, priests and deacons.
As for the original Latin terms there is ordinatio which means incorporation in to an ordo. Ordos are groups within the Church that are inducted into that specific group. This is done by a means of ordination which comes from the word ordinatio.
Today ordination is reserved for the sacramental act of integrating a man into the order of bishops, presbyters (priests) or deacons. This integration is above a simple election or delegation from the community because it confers a gift of the Holy Spirit (grace) that permits the exercise of the sacred power which can only come from Jesus Christ (Matthew 28:18-20).