My Definition of God

God is that which is fundamentally responsible for our existence. All Life, Planets, Stars, Galaxies, etc. What some religions would call “The Creator”.  Others might refer to Allah.
There is no proof that there is a being behind this, and there is no proof that there is not.
In this definition we are not making assumptions. We exist, we did not create ourselves, so whatever process or root cause resulted in our existence, we are referring to as God.

Note: By this definition, no human can be referred to as God. Nor can we attribute God like qualities to any natural phenomena. For they are all creations, and cannot therefor be the creator. Not Buddha, Ra, Caesar, or Jesus Christ.