From The Art and Popular Culture Encyclopedia
Secularization or secularisation generally refers to the transformation by which a society migrates from close identification with religious institutions to a more separated relationship. It is also the name given to a general belief about history, namely that the development of society progresses toward modernization and lessening dependence on religion as religion loses its position of authority.
Secularization has many levels of meaning, both as a theory and a historical process. Social theorists such as Karl Marx, Sigmund Freud, Max Weber, and Émile Durkheim, postulated that the modernization of society would include a decline in levels of religiosity. Study of this process seeks to determine the manner in which, or extent to which religious creeds, practices and institutions are losing their social significance (if at all).
The term also has additional meanings, primarily historical. Applied to church property, secularization involves the abandonment of goods by the church where it is sold to purchasers after the government seizes the property, which most commonly happens after reasonable negotiations and arrangements are made. In Catholic theology, the term can also denote the permission or authorization given for an individual (typically clergy, who become secular clergy) to live outside his or her religious colony (monastery), either for a fixed or permanent period.