Religion

Durkheim, 1912
A religion is a unified system of beliefs and practices relative to sacred things, that is to say, things set apart and forbidden -- beliefs and practices which unite into one single moral community called a Church, all those who adhere to them.

Durkheim, Emile. The elementary forms of the religious life. 1965 (1912):62

Bellah, 1964
A set of symbolic forms and acts which relate man to the ultimate condition of his existence.

Bellah, Robert N. "Religious evolution." American Sociological Review 29 (June): 258-374. 1964:358

Geertz, 1973
(1) a system of symbols which act to (2) establish powerful, pervasive, and long-lasting moods and motivations in men by (3) formulating conceptions of a general order of existence and (4) clothing these conceptions with such an aura of factuality that (5) the moods and motivations seem uniquely realistic.

Geertz, C. The interpretation of cultures. New York: Basic Books. 1973:90

Pargament, 1997
A search for significance in ways related to the sacred.

Pargament, K. I. The psychology of religion and coping: Theory, research, practice. New York : Guilford Press. 1997:32