Major Orders in the Orthodox Church refers to the three degrees of ordained clergy: bishop, presbyter, and deacon. Persons who hold these offices are charged with the celebration of the divine services and the administration of Church life. They have received the grace of the Holy Spirit to perform these jobs through the mystery of Holy Orders.
The first and highest degree of the clergy is the bishop (episkopos in Greek, which means overseer). He is the successor to the Apostles in the service and government of the Church. A bishop is responsible for and the head of all the parishes located in his diocese. All authority of the lower orders of clergy is derived from the bishop.
The second degree of the clergy is the presbyter, or priest. The presbyter governs a particular parish by the authority and with the blessing of his bishop. The presbyter blesses all of the divine services conducted in his parish and is authorized to celebrate all of the mysteries (sacraments) of the Church, with the exception of ordination, which is reserved to the bishop. The priest supervises all persons holding any office in his parish, including a deacon.
The third and lowest degree of the major orders of clergy belongs to the deacons. The word deacon means server and originally it referred to a person who waited on tables. The deacon ministers to the priest and bishop in the Divine Services and assists in the celebration of the mysteries of the Church. A deacon may not, however, celebrate the mysteries by himself.