Allah (ﷲ): This is the main name for God in the Qur’an. Indeed, this is the main name of God in Arabic used by Muslims and non-Muslims alike. For example, in an Arabic edition of the Bible, the word ‘Allah’ is used for God. In the Qur’an, Allah is mentioned 2816 times (including its variations such as lillah, tallah, billah and Allahuma). There are different views about the origin of this term.
The most plausible view seems to be that it is the abbreviated form of al-ilah. In Arabic, al- is the definite article and ilah means god. To be more precise, ilah is derived from the root "a-la-ha", which means ‘worship’. Thus, ilah means what is worshipped or worthy of being worshipped, just like kitab, which means what is written or what can be written.
The standard formulation of faith in Islam involves the declaration of two facts: La ilaha illallah and Muhammadur- Rasulullah. (There is no god but God and Muhammad is His messenger). As indicated in the Qur’an, it is clear that there have always been false gods. So when it is said, ‘There is no god but God’ it is obvious that it means, ‘There is no real god or no one worthy of worship but God’.
Ilah (إِلهَ): This is mentioned 120 times. In 37 cases, it is used for false gods. In the rest, it is either used for God specifically or in the general sense. For example, the Qur’an says:
“Were you witnesses when death approached Jacob, when he said to his children, ‘What will you worship after me?’ They said, ‘We will worship your god (God), and the god (God) of your fathers, Abraham, Ishmael, and Isaac, the one god (One God), and to Him do we submit.’” (2:133)
“Your god (God) is the one god (One God), there is no god except Him, the All-beneficent, the All- merciful.” (2:163)
Rabb (رَب): In Arabic, the term rabb means lord. It is mostly used for God, but it may also be used in a broader sense to be synonymous with master, guardian or owner. In the Qur'an, this term has been used for God 963 times. This shows the utmost importance of this quality of God. The only word that is used more frequently to denote God in the Qur’an is Allah.