Apostasy
Apostasy (Greek απο, apo, "away, apart", στασις, stasis, "standing") is the formal renunciation of one's religion. In a narrow sense, the term refers to renunciation and criticizing one's former religion. One who commits apostasy is an apostate, or one who apostatises. One of possible the reasons for this renunciation is loss of faith. Excommunication is a form of apostasy.
Many religious movements consider it a vice, a corruption of the virtue of piety in the sense that when piety fails, apostasy is the result. However, most converts to a new religion can also be considered apostates from a previous belief. The word is also used to refer to renunciation of belief in a cause other than religion.
Several religious movements punish apostates. Apostates may be shunned by the members of their former religious group. This may be the official policy of the religious group or may happen spontaneously. In Islam the prescribed punishment for apostasy is death.
Some Atheists and agnostics use the term deconversion to describe loss of faith in religion. Freethinkers do not see it as a loss. They see it as gaining rationality and respect for the scientific method.