How do you define religion?

Something I have been thinking about lately is what makes an organization a "religion" rather than a charity, social club, activist group, etc.? From time to time I hear that some Unitarian Universalist church is in danger of losing its tax-exempt status because they do not require that one believe in a supreme being with supernatural powers. Of course, I'm sure that these challenges typically have more to do with the fact that UUs are often activists for issues of social justice, and don't tend to vote Republican. Having spent two years at a Unitarian Universalist church here in Columbus, I would never hesitate to call it a "real" church, but I'm not sure how to explain why I think so. Then today on a break at work, I saw a story in the Faith and Values section of the Columbus Dispatch about Universism. The article states that the only "rule" of Universism is "do not harm one another". In the article, the founder of Universism, 28-year-old medical student Ford Vox says "It's a matter of looking at it not as a transcendent truth that is immutable. Our central tenet is that truth is mutable and changes and depends on our own perception." How do you define religion? This is a question I am just putting out there for discussion, and I hope it is of interest to people. At the moment, I don't have an answer of my own to that question, so I am very interested in knowing what the rest of you have to say.