I was asked a multiple part question: "Who, what, and where is G-d?" I was thinking this is pretty simple. Who is G-d? He is the G-d of Abraham, Yitzhak, and Yaakov. Where is G-d? Everywhere. To say otherwise would be to place limits on G-d. However, when it came to the question, "What is G-d," I was at loss for words. I know what G-d is not, but what exactly is G-d? Is He simply everything that He is not, or is there a more precise answer to this question?
We cannot say what G-d is because G-d is not a created object. But we can describe some of His attributes.
For instance G-d is: [i]
Before (anything was created)
After (everything will be over)
Also, since we are commanded to emulate Hashem we have to know what He is like. For instance, Hashem is:
Jealous (i.e. will not tolerate idolatry)
[i] In no way is this intended to be a complete list