I guess I will throw my 2c in.
I THINK (i will try not to hurt myself) that since we have no evidence (please look up that word if you don't know what it means) of G/god the definition is the perception one has. If one is a theist it would be something similar to a traditional concept of an all powerful being / creator etc, etc... If one is an atheist I imagine it would be a unprovable concept which they refuse to believe in because there is no evidence. Still further there is the concept that god is anything you place in the position of personal importance traditionally held by the theist's "god".
Me personally I do believe there is a god/creator but I do not believe in the traditional concepts which many hold to. I feel there is a reason/source/cause for the order we see in the universe but I do not believe that this source has the pettyness that people ascribe to it.
-r