"There is a thing inherent and natural, which existed before heaven and earth. Motionless and fathomless, It stands alone and never changes; It pervades everywhere and never becomes exhausted. It may be regarded as the Mother of the Universe. I do not know its name. If I am forced to give it a name, I call it Tao, and I name it as supreme."
The Tao is a philosophical idea that's hard to describes in words by Lao Zi who was the founder of the philosophy/religion of Taoism. But the idea is rather close to natural order of the universe itself. And much different in idea than most religions have with one creator-deity that simply created the sun, the moon, and our little blue marble but apparently forgot to tell us about the rest of the universe.