Clergy are formal leaders within established religions. Their roles and functions vary in different religious traditions, but usually involve presiding over specific rituals and teaching their religion's doctrines and practices. Some of the terms used for individual clergy are clergyman, clergywoman, clergyperson, churchman, ecclesiastic, and cleric, while clerk in holy orders has a long history but is rarely used. In Christianity, the specific names and roles of the clergy vary by denomination and there is a wide range of formal and informal clergy positions, including deacons, elders, priests, bishops, preachers, pastors, presbyters, ministers, and the pope. In Islam, a religious leader is often known formally or informally as an imam, caliph, qadi, sheikh, mufti, mullah, muezzin, or ayatollah. In the Jewish tradition, a religious leader is often a rabbi (teacher) or hazzan (cantor). The word cleric comes from the ecclesiastical Latin Clericus, for those belonging to the priestly class. In turn, the source of the Latin word is from the Ecclesiastical Greek Klerikos (κληρικός), meaning appertaining to an inheritance, in reference to the fact that the Levitical priests of the Old Testament had no inheritance except the Lord. "Clergy" is from two Old French words, clergié and clergie, which refer to those with learning and derive from Medieval Latin clericatus, from Late Latin clericus (the same word from which "cleric" is derived). "Clerk", which used to mean one ordained to the ministry, also derives from clericus. In the Middle Ages, reading and writing were almost exclusively the domain of the priestly class, and this is the reason for the close relationship of these words. Within Christianity, especially in Eastern Christianity and formerly in Western Roman Catholicism, the term cleric refers to any individual who has been ordained, including deacons, priests, and bishops. In Latin Catholicism, the tonsure was a prerequisite for receiving any of the minor orders or major orders before the tonsure, minor orders, and the subdiaconate were abolished following the Second Vatican Council.