On the nature of religion

Sometimes, in the midst of a deep philosophical conversation on the subject, the question pops into my head "What is religion?" See, I don't think we're always on the same page about what it is. Dictionary.com - with which I agree - defines religion as "a set of beliefs concerning the cause, nature, and purpose of the universe". But do other people agree with that definition? I get the impression from some that they feel that religion, at least in its primary scope, is almost devoid of belief, that belief is separate. That sort of fits in with definition 3, "the body of persons adhering to a particular set of beliefs and practices", but even here, "beliefs and practices" are key.

Is religion a group phenomenon, or personal? Is it about belief, or about ritual?