Theories of religion offer various explanations for the origins and workings of religion.
The modern concept of "religion" as an abstraction which entails distinct sets of beliefs or doctrines is a recent invention in the English language since such usage began with texts from the 17th century due to the splitting of Christendom during the Protestant Reformation and more prevalent colonization or globalization in the age of exploration which involved contact with numerous foreign and indigenous cultures with non-European languages.
Even in the 1st century AD, Josephus had used the Greek term ioudaismos, which some translate as "Judaism" today, even though he used it as an ethnic term, not one linked to modern abstract concepts of religion as a set of beliefs.
Throughout its long history, Japan had no concept of "religion" since there was no corresponding Japanese word, nor anything close to its meaning, but when American warships appeared off the coast of Japan in 1853 and forced the Japanese government to sign treaties demanding, among other things, freedom of religion, the country had to contend with this Western idea.
According to the philologist Max Müller in the 19th century, the root of the English word "religion", the Latin religio, was originally used to mean only "reverence for God or the gods, careful pondering of divine things, piety" (which Cicero further derived to mean "diligence").
Religion is a cultural system of behaviors and practices, world views, sacred texts, holy places, ethics, and societal organisation that relate humanity to what an anthropologist has called "an order of existence".
Religious practices may include rituals, sermons, commemoration or veneration (of God or deities), sacrifices, festivals, feasts, trances, initiations, funerary services, matrimonial services, meditation, prayer, music, art, dance, public service, or other aspects of human culture.
Religions have sacred histories and narratives, which may be preserved in sacred scriptures, and symbols and holy places, that aim mostly to give a meaning to life.
Religions may contain symbolic stories, which are sometimes said by followers to be true, that have the side purpose of explaining the origin of life, the Universe, and other things.
Traditionally, faith, in addition to reason, has been considered a source of religious beliefs.
With the onset of the modernisation of and the scientific revolution in the western world, some aspects of religion have cumulatively been criticized.
Though the religiously unaffiliated, including atheism (the rejection of belief in the existence of deities) and agnosticism (the belief that the truth of certain claims – especially metaphysical and religious claims such as whether God, the divine or the supernatural exist – are unknown and perhaps unknowable), have grown globally, many of the unaffiliated still have various religious beliefs.
The study of religion encompasses a wide variety of academic disciplines, including theology, comparative religion and social scientific studies.