Is religion a common noun or collective noun?

The word religion is a common noun, a general word for a belief in a god or in a group of gods; a general word for an organized system of beliefs, ceremonies, and rules associated with such a belief; a word for any religion of any kind.

A collective noun is a noun used to group nouns for people or things in a descriptive or fanciful way; for example, a congregation of worshipers or a a mass of priests.