A cleric is:
The term "cleric" simply means a member of the clergy. Its non-specific nature means it is often used to refer to the religious leadership in Islam, where "priest" is not accurate and where terms such as "imam" are not widely understood.
The term "clerk" derives from "cleric", since in medieval times the clergy were one of the few groups who could read, and therefore were often employed to do bookkeeping and similar work. The term "clerical work" continues to this day to refer to such functions.
In Role-playing Games
Few popular entertainments give as prominent a role to members of the clergy as do Dungeons & Dragons and the many similar entertainments that descended from it. Most games in a fantasy setting feature members of religious orders of various kinds, who get magical powers from the gods that figure in the setting for the game. These games employ the term "cleric" since members of the character class include numerous types of clergy, not all of which might be covered by a more specific term such as "priest".
Clerics are valuable members of an adventuring party in these games. Most systems give the cleric healing powers to heal wounds suffered by player characters in the games, and sometimes, to raise characters from the dead. In most systems, clerics also enjoy powers to banish the undead assailants of the adventurers. Many games also allow evil clerics, the followers of evil deities, who wield similar but contrary powers to bring poison and disease against the adventurers, and who create undead armies to oppose them.
Clerics operate under a number of restrictions. They typically must retain the alignment appropriate to their faith and ethos, and may lose their clerical powers if they stray from an approved code of behaviour. Many must tithe their adventuring treasures to a temple or similar institution. In many systems, clerics are restricted in the sort of weapons they can bear; the most common restriction, taken from European history, forbids the use of edged weapons such as swords. (The 3rd edition of Dungeons & Dragons has lifted most of these restrictions from the cleric. For example, clerics are no longer restricted to bludgeoning weapons, making the cleric class less tied to European roots.)
Related to the cleric is the paladin, who in these games is typically a warrior aligned with a religious order, and who uses his martial skills to advance its holy cause.