As Muslims, we understand that there is no god but God, and there is nothing that compares to Him. He is the Creator, and He is not, nor does He ever become, part of His creation.
We often hear people say, "I don't know if I really believe in God, but I do believe in a Higher Power." Many people hesitate to say "God" because, for them, the word conjures the image of an old man with a long white beard and robe, floating on a cloud. You've probably seen this guy in renaissance art. This Zeus looking character is NOT God. God is not an old man or a young man or a spirit or a ball of energy or a statue or any physical thing. He is the Eternal Creator and Sustainer of everything that exists, He is One with no partner, He has power over all things, and none has the right to be worshipped but Him. Doesn't that make a lot more sense?
"In the name of Allah, the Most Merciful, the Ever-Merciful
Say, 'He is Allah, One,
Allah, the Self-Sufficient Eternal Refuge.
He does not beget and He is not born,
and there is nothing comparable to Him.'”
Only a relatively small percentage of Muslims speak Arabic as their first language, yet Muslims around the world use the same word for God: Allah. But why? Why not just use the word for God in our own languages? One reason is that, since the Quran was revealed in Arabic, and Arabic is used by Muslims multiple times a day in prayer, the word has something of a unifying quality for Muslims. No matter where we're from, no matter what language we speak, Allah is one word we can all understand. While there is nothing wrong with using other words for God, most Muslims are accustomed to using the word Allah, and many prefer to use the word Allah over the word for God in their own language. However, a deeper reason that many cite is the unique quality of the word Allah. Look at English word God. We spell it with a capital G and it means the One True God, but make it a lower case g and it could be referring to Zeus, Ganesh, Thor, or anything that people worship. Since capitalization does not come across in speech, there is no way to distinguish between God and... god. If you add an s it becomes gods plural, and it can become male or female, god or goddess. In contrast, the Arabic words for god and God are two different words. Lowercase god is ilah and capital God is Allah, so when you say Allah there is no confusion. On top of that, the word Allah is unlike most Arabic words in that it cannot be made plural nor take gender. So when you say "Allah" there is no doubt that you are talking not about one of many gods, but about the One and Only God, not a man or a woman but the Creator of men and women, capital G-o-d, God.
"And to Allah belong the best names, so invoke Him by them." -Qur'an 7:180
Some people mistakenly think that Allah is the "god of the Muslims," and a few even like to claim that Allah is an Arabian moon god, but the word Allah is simply the Arabic word for God. Every language has a word for God, and Arabic is no exception. If you have any doubt, you can check an Arabic translation of the Bible, you will find that it uses the word Allah. In fact, since Arabic is a Semitic language like Hebrew, the language of the Torah, and Aramaic, the language spoken by Jesus (pbuh), you'll find that the words for God in those languages, El in Hebrew and Alaha in Aramaic, are very similar to the word Allah. This just goes to show that Allah is the same One God, the Creator of the Universe, loved and worshiped by all of God's prophets.
"He is Allah , the Creator, the Inventor, the Fashioner; to Him belong the best names." -Qur'an 59:24