“Among the people are those who dispute about God without any knowledge, and follow every forward devil” (The Qur‘an, 22:3)

In Islam, God is known by many names: The Just, The Merciful, The Creator, among others. 
Nonetheless, according to the Qur‘an, Allah, the Arabic word for God, is commonly used and is considered the prevailing .
The linguistic root of Allah indicates that He is the one and only Being worthy of worship and obedience.  Allah is therefore, according to Islamic tradition, considered to be the all-encompassing word to express this principle, chosen by God Himself, and so revealed through Muhammad, his messenger.  It is therefore normally preferred by Muslims. 
Linguistically Allah is a unique word.  It is generic and singular, and has no conjugation. This word reflects the singular Oneness as a concept of God, for Muslims, for whom God is not contained within a trinity.  He did not incarnate in a son who died for mankind.  He does not reside in Heaven removed from the affairs of the world. He is not revealed in human form. In Islam, God is One, Unique and Singular.  He has no mother or father, no children, no companions, no associates, and is like nothing and no one else.  He is not represented by any means, or object, or figure, he is not worshipped in any form or physical manifestation.  God has no limits, he is not found in any geographical location, neither on Earth nor in Heaven and no place may be regarded as containing Him, yet nowhere is without Him or far from Him.  He is Light, to be found everywhere, but without a defined presence. 

“Look! To God indeed belongs whoever is in the heavens and whoever is on the earth. And what do they pursue who invoke partners besides God? They merely follow conjectures and they just make surmises. It is He, who made the night for you that you may rest in it, and the day to provide visibility. There are indeed signs in that for people who listen. They say, ‘God has taken a son!‘ Immaculate is He! He is the All-sufficient. To Him belongs whatever is in the heavens and whatever is in the earth. You have no authority for this [statement]. Do you attribute to God what you do not know?” (The Qur‘an, 10:66-68) 

“And God has said; do not take to yourself two gods. He is only one god; so have awe of me. 'To him belongs all that is in the heavens and the earth. This is the religion for ever. Would you then fear any but God?” (The Qur‘an, 16:51-52) 

Worthy of mention, at this point, is the reference from the Old Testament, which coincides with this description: 

 “So keep watch on yourselves with care; for you saw no form of any sort on the day when the voice of the Lord came to you in Horeb out of the heart of the fire: So that you may not be turned to evil ways and make for yourselves an image in the form of any living thing, male or female, Or any beast of the earth, or winged bird of the air, Or of anything which goes flat on the earth, or any fish in the water under the earth.” .”  (The Bible, Deuteronomy 4:15-18,) 
 
“All this he let you see, so that you might be certain that the Lord is God and there is no other. Out of heaven itself his voice came to you, teaching you; and on earth he let you see his great fire; and his words came to your ears out of the heart of the fire (…) So today be certain, and keep the knowledge deep in your hearts, that the Lord is God, in heaven on high and here on earth; there is no other God.”  (The Bible, Deuteronomy 4: 35-39) 

In truth, even the millions of Arab-speaking Christians have no other word for God than “Allah”.