What makes a religion?

[robvalue]

Religions are tricky things to nail down. I've been thinking about what makes a set of beliefs into a religion. What is the minimum requirement? Of course religions tend to make claims about the origin and/or nature of reality, but is that necessary?

The best I can come up with is that a religion must include firmly held beliefs that are speculative: beyond what can demonstrated to be (most likely) true.

If there is no speculation, then all you have is a set of evidence based beliefs. It would seem ridiculous to call that a religion.