Religion (Noun)

1. a set of beliefs concerning the cause, nature, and purpose of the universe, esp. when considered as the creation of a superhuman agency or agencies, usually involving devotional and ritual observances, and often containing a moral code governing the conduct of human affairs.
2. a specific fundamental set of beliefs and practices generally agreed upon by a number of persons or sects: the Christian religion; the Buddhist religion.
3. the body of persons adhering to a particular set of beliefs and practices: a world council of religions.

* Excerpted from the Random House Webster's Unabridged Dictionary 3.0.

Note that we are concerned here primarily with the third definition, and even then we would prefer the definition to read "identified with" instead of "adhering to".