Question: Who is Allah? Is Allah just another word for God?
Yes, Allah and God are one and the same. "God" is the English equivalent of "Allah". Arabic speaking Christians use the word "Allah", when referring to God. On the same lines, when using Spanish, we would say "Dios", or in French, "Dieu".
It does not matter what name we use for God, for God Himself says in Quran, to Him belong the most beautiful names.
[Quran 17:110] Say, "Call Him GOD, or call Him Most Gracious; whichever name you use, to Him belongs the best names." ...
[Quran 7:180] To GOD belongs the most beautiful names; call upon Him therewith, and disregard those who distort His names. They will be requited for their sins.
This is commonly accepted, for example, Wikipedia also independently says this.
Peace