If we talk about the definition of the priesthood, this is one of the three priestly orders of the Catholic Church, by which the deacon receives the dignity and attributions proper to the presbyter, or
priest.
"Holy Orders is the sacrament by which the mission entrusted by Christ to his apostles continues to be exercised in the Church until the end of time: it is, therefore, the sacrament of the apostolic ministry. It comprises three degrees: the episcopate, the presbyterate and the diaconate."
The priesthood "goes beyond a simple election, designation, delegation or institution by the community, for it confers the gift of the Holy Spirit that allows the exercise of a 'sacred power' that can only come from Christ, through his Church."
Catechism, 1536-1538.