It really depends on who you ask. I recall reading somewhere that someone had collected 27 “authoritative” definitions , and among those, there wasn’t a single definition that had no mutually exclusive definition.
Simple dictionary definitions will tell you that religion includes a belief in the supernatural, and while it’s true that most religions do to some degree, not all religions do. Wikipedia takes several hundred lines of text to tell you that the experts can’t agree on a universal definition of religion, but does present a range of definitions.
It does include one definition that I thought came close to the mark:
According to the MacMillan Encyclopedia of Religions, there is an experiential aspect to religion which can be found in almost every culture:
[…] almost every known culture [has] a depth dimension in cultural experiences […] toward some sort of ultimacy and transcendence that will provide norms and power for the rest of life. When more or less distinct patterns of behavior are built around this depth dimension in a culture, this structure constitutes religion in its historically recognizable form. Religion is the organization of life around the depth dimensions of experience—varied in form, completeness, and clarity in accordance with the environing culture.
I liked this definition because it doesn’t assume sacred tomes, deities, creeds, an afterlife or anything of a supernatural nature. For me its weakness is in the use of the phrase “historically recognizable form“. I’m not sure that all religions today would conform with a historically recognisable form of religion. And it makes no allowance for future forms that religion might take.
However, Sir Lloyd Geering has come up with a simple, short definition that, according to him, covers all religion, past, present and future. His definition is:
A total mode of the interpreting and living of life.
Sir Lloyd explains:
Everybody who takes life seriously, in my view, is taking the first steps in religion. And this definition of religion, fortunately, covers all the types of religions we’ve had or will have in the future, because it recognises that religion is a human product. Religion is what we humans have evolved in our culture to enable us to make meaning of life, and to live together in the most harmonious way.
The clip below is from a discussion with Sir Lloyd Geering at Auckland Museum’s LATE at the Museum Innovation series in 2010. It’s moderately long at 20m 13s. Sir Lloyd starts speaking at 3:14 if you’d like to skip the introduction. He discuses what is meant by “the divine”; the problem with the word “God”; what religion is; the rise of “popular atheism”; NZ secularism vs US fundamentalism; the Green movement as a type of religion; and much more: