How is the dao defined? how does it compare with a god or gods in other religions?

Daoists take the center way, with adjusting and no extremes. This is like Aristotle, who felt that ethics were the center way between two extremes. 
Daoism has the Ying and the Yang, dull and light, male and female as the focal point of all things. Daoism does not have the god or divine beings. It is a logic. The reason they all have symbols that they venerate is that Daoism got blended with animism and neighborhood people religion. The author of Daoism was a monotheist, however, a divine being was never the principal thought in Daoism.