In the Latter Day Saint movement, priesthood is the power and authority of God given to man, including the authority to perform ordinances and to act as a leader in the church. A group of priesthood holders is referred to as a quorum.
Priesthood denotes elements of both power and authority. The priesthood includes the power Jesus gave his apostles to perform miracles such as the casting out of devils and the healing of sick (Luke 9:1). Latter Day Saints believe that the Biblical miracles performed by prophets and apostles were performed by the power of priesthood, including the miracles of Jesus, who holds all of the keys of the priesthood. The priesthood is formally known as the "Priesthood after the Order of the Son of God", but to avoid the too frequent use of the name of deity, the priesthood is referred to as the Melchizedek priesthood (Melchizedek being the high priest to whom Abraham paid tithes).
As an authority, priesthood is the authority by which a bearer may perform ecclesiastical acts of service in the name of God. Latter Day Saints believe that acts (and in particular, ordinances) performed by one with priesthood authority are recognized by God and are binding in heaven, on earth, and in the afterlife. In addition, Latter Day Saints believe that leadership positions within the church are legitimized by the priesthood authority. The Church of Jesus Christ of Latter-day Saints (LDS Church), the largest church in the movement, restricts its priesthood to men, as do most of the other Latter Day Saint denominations. An exception is the Community of Christ, the second largest denomination of the movement, which began ordaining women to all of its priesthood offices in 1984.