Allah is the word for God that has always been used in Arabic translations of the Bible. Allah is much closer to the ancient Hebrew and Aramaic words found in the original languages than the English word “God”.
More even than that... The name "Allah" is literally "The God" ("al-" the definite article "the", and "ilah" meaning god).
Its use as a name of (a monotheistic) God has been recorded and documented back to 500 B.C. -- a THOUSAND years before Islam.
Its use as a proper name (by Islam for their god) is analogous to our (Christian) use of "God" as the proper name of the God of Abraham, although the Tetragrammaton, Yahweh, and other names also are correct for the Christian God.
But like everything else it touches, Islam will step all over and corrupt the ancient word and its usage, claiming it solely for itself. It is one of the most historically-ignorant, intolerant "religions" in the history of the world.