Folk religion consists of ethnic or regional religious customs under the umbrella of an organized religion, but outside of official doctrine and practices.Don Yoder has defined "folk religion" as "the totality of all those views and practices of religion that exist among the people apart from and alongside the strictly theological and liturgical forms of the official religion."

The term "folk religion" is generally held to encompass two related but separate subjects. The first is the religious dimension of folk culture, or the folk-cultural dimensions of religion. The second refers to the study of syncretisms between two cultures with different stages of formal expression, such as the melange of African folk beliefs and Roman Catholicism that led to the development of Vodun and Santería, and similar mixtures of formal religions with folk cultures.

Chinese folk religion, Folk Christianity, Folk Hinduism, and Folk Islam are examples of folk religion associated with major religions. There is sometimes tension between the practice of folk religion and the formally taught doctrines and teachings of a faith.^{[citation needed]} In other cases, practices that originated in folk religion are adopted as part of the official religion.^{[citation needed]} The term is also used, especially by the clergy of the faiths involved, to describe the desire of people who otherwise infrequently attend religious worship, do not belong to a church or similar religious society, and who have not made a formal profession of faith in a particular creed, to have religious weddings or funerals, or (among Christians) to have their children baptised.