The term "Cleric" is used to describe members of a religious order who serve a god. Specifically members that have taken vows and are bound to a deity as opposed to those who are simply worshipers or lay associations.
The most widely known clerics are a deity's priests; however most religions have other other more secular members who are also pledged to the deith. These members may have different skill sets, functions and may or may not be mana wielders. Those that are mana wielders channel mana in the same way as priests, the primary differences is that they typically don't conduct Worship rituals and collect mana from worshipers.
The exact names may vary from religion to religion and not all religions have all positions, and some may have more, but below are the most common clerical types.
Priests: Priests are the principle agents of the deities on Astlan. They conduct Worship and collect offerings of mana, animus and money from worshipers. They also provide healing, religious instruction, mentoring, care and other services as required.
Monks: Monks are typically male members of the religion who have taken vows of loyalty and are linked to the deity; they are not, however, typically Illuminaries. Illuminaries are people who collect and funnel mana and animus upstream to a deity. Monks are often craftsmen for the church, clerks, scholars, sages and in some religions, warriors.
Nuns: Nuns are typically female members of the religion who have taken vows of loyalty and are linked to the deity. Like monks, they are not typically Illuminaries. In many religions Nuns perform healing and care taking roles at the instruction of the priests. Like monks they may also be craftsmen, clerks, scholars and sages, and again like monks, warriors in some religions.
Holy Warriors: Holy warriors are military units of churches. Not all churches have armies, but if they do this is how they are typically classified. Vows and linkage to the deity depend on religion and level, in some cases no particular vow is needed and the soldiers are simply in the employ of the church, although typically the are also worshipers. Higher rank soldiers typically have greater devotion and typically have vows and linkages and are thus true clerics as well as soldiers.
Holy Knights: Holy Knights are knights who may or may not be of noble birth. Holy Knights are formally invested by a high ranking member of the priesthood (typically higher than a priest). Depending on the knight, religion and their rank, knights may or may not channel mana from the deity. If they do, their rituals and chants are generally of a martial nature for either offensive or defensive purposes when fighting the enemies of the church.