The only God Jews, Christians and Muslims worship is one, who is Allah as mentioned in the Holy Quran:
Say: O People of the Scripture! Come to an agreement between us and you: that we shall worship none but Allah, and that we shall ascribe no partner unto Him, and that none of us shall take others for lords beside Allah. And if they turn away, then say: Bear witness that we are they who have surrendered (unto Him). (64) Al Imran 3:64
These religions emerged in the Middle East and the Holy Books of these religions were written in the native languages. But, God is an English word. According to the Free Dictionary, God is:
the sole Supreme Being, Creator and ruler of all, in religions such as Christianity, Judaism, and Islam.
Arab Jews and Christians in Arabia and North Africa call God Allah.
But, was God as a name mentioned in the previous scriptures? Read this article, Islamic Marcionism in Malaysia: Is Allah Equivalent to God?, by Joachim Martillo which is posted on the American Muslim Website.