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Here is a clear, authoritative answer, a discussion of the classifications of the ordained leadership of the Church since the 2nd century. One excerpt:

Priests (presbuteroi) are also known as "presbyters" or "elders." In fact, the English term "priest" is simply a contraction of the Greek word presbuteros. They have the responsibility of teaching, governing, and providing the sacraments in a given congregation (1 Tim. 5:17; Jas. 5:14–15).

Of course, as the Catechism of the Catholic Church makes clear, the central liturgical celebration of Catholicism, the mass, is regarded as

The Holy Sacrifice, because it makes present the one sacrifice of Christ the Savior and includes the Church's offering. The terms holy sacrifice of the Mass, "sacrifice of praise," spiritual sacrifice, pure and holy sacrifice are also used, since it completes and surpasses all the sacrifices of the Old Covenant.

The priest, representing Christ, presides over this liturgical sacrifice.