Spirituality and religion are, at least in part, overlapping concepts. They are highly complex and hard to define, and their exact relationship is difficult to describe. Today, they are used in a whole number of different academic disciplines (theology, religious and cultural studies, psychology, sociology, historical studies, etc.), in many different contexts, and in reference to different traditions or religions in different parts of the world. Yet their meaning and much of the scientific discussions about them in the past has been strongly influenced by European and Western Christianity and, in part, Judaism and Islam that accounts for some of the difficulties that currently are of central concern for many researchers in this increasingly international, multireligious, and open field of study. In addition to the broad long-term historical context that has shaped these concepts, there are contemporary social and cultural developments that have created a new interest in spirituality, which, more and more, is seen as clearly different from religion, in relationship to children and adolescents but also with adults.
The etymology of the concepts is telling but does not lead to consensual understandings or to clear definitions that can be relied upon in the present. Both terms go back to Latin roots. While the adjective spiritual may be traced back, as a translation, to the Greek (New Testament) pneumatikos, or pneumatic-relating to the pneuma or spirit (which again is rooted in the Hebrew bible's notion of ruach or spirit), the noun spirituality does not occur before the fifth century and becomes a common concept not before the 12th century. It is first used in a Christian context (baptism and Christian life after baptism), later in a more general sense to describe that which is different from body or matter and which is not subject to temporal limitations. The medieval connotations of the concept remain Christian in a broad sense, later, after the Reformation, more Roman Catholic than Protestant because of the special emphasis on spiritual discipline in Catholicism, for example, with the Jesuits. Today, the concept is used in all Christian denominations and also within Judaism, Islam, Buddhism, Hinduism, as well as in other traditions and religions in order to describe the spiritual aspects of these religions or traditions or to refer to special groups or orientations within these religions or traditions.
The origins and meaning of the term religion are doubtful, with Cicero connecting it to relegere, or to read over again, and other authors like Augustine to religare, or referring to binding obligation. Under the influence of early Christianity, the general concept of religion soon became identified with the Christian faith and was then used in opposition to what, from a Christian perspective, was seen as heathen idolatry and aberrations. It is only in modern times that the concept religion is applied, as a universal term, to all religions interchangeably and independently of different traditions, truth claims, and convictions, and religious practices.
In the contemporary literature, it is often stressed that there are no clear or consensual definitions of the two concepts. Most of the numerous definitions found in the literature are based on a certain normative understanding or on the wish to see a certain understanding prevail, not only in theory but also within the life of religious traditions or communities. The universal application of the concepts presupposes that their meaning is mostly independent of certain content but rather refers to general or universal functions or structures, like finding, expressing, or creating ultimate meaning, world coherence, cosmic order, foundations of ethical life, etc. According to this point of view, it is the specific function for the individual or for a group or community or society that defines the meaning of religion and spirituality. In contrast to this, the older literature also includes content-related features within the universal use of the concepts, for example, worship of a goddess or higher being. These kinds of content-related universals are now often criticized as illegitimate generalizations from Judaism, Christianity, and Islam to nontheistic or polytheistic religions. Comparative study of religion and spirituality is legitimate, but one must always be mindful of the origin of the concepts applied as well as of their being influenced and loaded by particular traditions and cultural settings. So-called indigenous religions or spiritual traditions, for example, in Africa or Asia cannot be adequately captured by making them fit into Western categories.