Amazingly, we seldom define the fundamental aspects of life. The difference between men is not whether they are religious or not but what kind of religion they have. All religions focus either on man or on God.
All religion has a set of beliefs about where the universe came from, what it is, and why it exists.
That's all that religion is. Atheism is a religion that believes the universe is the product of natural forces. Many religions which claim to believe in God or gods are also humanistic, for they do not focus on any authority higher than man. The only authority they seek for what they do is what makes them feel good or what is popular with other men. It could be polytheistic or monotheistic, but it believes in a higher authority.