An infidel (literally "unfaithful") is a person who is accused of disbelief in the central tenets of one's own religion, such as members of another religion, or irreligious people.
Infidel is an ecclesiastical term in Christianity around which the Church developed a body of theology that deals with the concept of infidelity, which makes a clear differentiation between those who were baptized and followed the teachings of the Church versus those who are outside the faith. The term infidel was used by Christians to describe those perceived as the enemies of Christianity.
After the ancient world, the concept of otherness, an exclusionary notion of the outside by societies with more or less coherent cultural boundaries, became associated with the development of the monotheistic and prophetic religions of Judaism, Christianity, and Islam (cf. pagan).
In modern literature, the term infidel includes in its scope atheists, polytheists, animists, heathens, and pagans.
A willingness to identify other religious people as infidels corresponds to preference for orthodoxy over pluralism.
The origins of the word infidel date to the late 15th century, deriving from the French infidèle or Latin īnfidēlis, from in- "not" + fidēlis "faithful" (from fidēs "faith", related to fīdere 'to trust'). The word originally denoted a person of a religion other than one's own, especially a Christian to a Muslim, a Muslim to a Christian, or a gentile to a Jew. Later meanings in the 15th century include "unbelieving", "a non-Christian" and "one who does not believe in religion" (1527).
Christians historically used the term infidel to refer to people who actively opposed Christianity. This term became well-established in English by sometime in the early sixteenth century, when Jews or Mohammedans (Muslims; formerly called saracens), were described contemptuously as active opponents to Christianity. In Catholic dogma, an infidel is one who does not believe in the doctrine at all and is thus distinct from a heretic, who has fallen away from true doctrine, i.