لا إله إلا الله
Lā ilāha illā Allāh
“There is no god but God”: the first part of the declaration of faith, said on all occasions.
What it means
This is the central statement of Islam. It means that no being has the right to be worshipped except God, and the Quran commands, “Know that there is no god but God” (47:19). It is the first half of the shahādah, the declaration of faith, which is completed by testifying that Muhammad (peace be upon him) is the Messenger of God. Muslims say it in daily remembrance (dhikr), in distress, and in the call to prayer, and a person who wishes to enter Islam declares it. A hadith reported by al-Tirmidhi calls it the best of remembrance. Its two parts, a denial and an affirmation, set aside every object of worship and then affirm God alone.
Often misunderstood as
The Arabic “Allah” is sometimes treated as the name of a god distinct from the God of other faiths, but the word simply means God, and Arabic-speaking Christians use it too.
Term and Arabic as listed in Ismail al Faruqi, Toward Islamic English (International Institute of Islamic Thought, 1995), p. 56, listed as LĀ ILĀHA ILLA ALLAH.. The definition is restated here.