Some competing definitions.
Immanuel Kant - religion is the recognition that all of our duties as divine commands.
Paul Tillich - religion is a matter of being grasped by an "ultimate concern" and contains the answer to the question of the meaning of our lives.
Max Stackhouse - religion a comprehensive worldview or 'metaphysical moral vision' that is accepted as binding because it is held to be in itself basically true and just, even if all dimensions of it cannot be either fully confirmed or refuted.
Emile Durkheim - religion is "a unified system of beliefs and practices relative to sacred things, beliefs and practices which unite into one single moral community called a church, all those who adhere to them."
Sigmund Freud - religion is a "childhood neurosis" and "wish fullfillment."
Karl Marx - religion is the sign of the oppressed creature, the opium of the people.
Richard Dawkins - belief in a personal god qualifies as a delusion.
Frederich Nietzsche - Faith means not wanting to know what is true. "The very word 'Christianity' is a misunderstanding — in truth, there was only one Christian, and he died on the cross.”
Vladimir Lenin - the yoke of religion that weighs upon mankind is merely a product and reflection of the economic yoke within society.