And, here, from my dissertation's section on "Definition of important terms," is that very definition.
22. Religion -- the holding of certain beliefs, and/or practice of certain behaviors, and/or set of human relationships, tending to revolve about the relationship of human beings to the power(s) of the cosmos, and to each other, where those relationships are seen to have a sacred dimension; any organized movement which practices a religion; a set of beliefs or principles or sacred stories which guides the individual or purports to explain the meaning or functioning of the cosmos in terms beyond the cosmos; also, a subculture within a larger group, whose members may identify with the subculture and its religious labels and/or symbols, but who themselves have a different, or inchoate, system of beliefs or values. The belief in a God or gods is important for most religions, but not necessary; there are religions where this belief is unimportant or thought to be absent. For the purposes of this study, the collection of ideas sometimes called "secular humanism" was not considered a religion.
-- Arthur W. Collins, "An Assessment of Religious Literacy Among Selected Groups of Secondary Students," ISU (1991), p. 17.
Okay, you try it. But remember, you have to include not only religion(s) you agree with, but heretical ones, primitive ones, classical ones, ones which are identified with but insincerely practiced ("cultural Christianity"), yada yada yada.
“When I use a word,” Humpty Dumpty said, in rather a scornful tone, “it means just what I choose it to mean—neither more nor less.” “The question is,” said Alice, “whether you can make words mean so many different things.” “The question is,” said Humpty Dumpty, “which is to be master—that’s all.”