What is a religion?

The question, what is a religion, is answered differently by many different people. This is my attempt to define religion in a way that both fits with the modern understanding of the concept, while also trying to be as objective and non-arbitrary as possible. My current definition can be worded as follows:

A religion is a system of rituals, expected behaviors, and supernatural beliefs.

Mandatory Elements

To reach this conclusion, I tried to tease out the mandatory elements of things traditionally described as religions. I don't think it is possible to call something a religion unless is is systemic, has rituals, expected behaviors, and belief in the supernatural. There can be all sorts of additional aspects, but these four elements must be present. Below I describe each element in detail.

Systemic

All religions are systemic. That is, they are built upon a structure and have an ordered flow. This is the bureaucracy that holds the religion together and ensures that the rituals, expected behaviors, and supernatural beliefs are all essentially the same for everyone in the religion. It usually includes a hierarchical power structure which is used to guide the religion and make rulings on which rituals, behaviors, and beliefs are "canon." Some religions are extremely systemic (in Catholicism, the Vatican has detailed their official position on pretty much everything), while others are much less systemic (Quakers are much less systemic, but they still have a basic structure). When there is a big enough disagreement to the system inside a religion, you get a schism and the religion splits in two.

If a religion stops being systemic, you get what people often call "spiritual, but not religious." That is, they still perform rituals, have expected behaviors, and believe in the supernatural, but there is no way to check to see if anything they're doing is "proper," so everything quickly becomes muddled and the rituals, behaviors, and supernatural beliefs become inconsistent and contradictory.

Rituals

All religion have rituals. I'm using the term "ritual" in a broad sense, including ceremonies, songs, dances, body movements, and the like.

Non-mandatory Elements

Prayer

These are the elements that, when removed from the equation, prevent something from being a religion. For example, many religions feature a form or prayer, however, would Islam still be a religion if Muslims stopped praying? I believe it would. However, would Islam still be a religion if it no longer included anything related to the supernatural (gods, spirits, souls, miracles, etc.)? I don't believe it would. Below I describe each of the attributes in detail.