The concepts associated with the term Allah (as a deity) differ among the traditions. In pre-Islamic Arabia amongst pagan Arabs, Allah was not the sole divinity, having associates and companions, sons and daughters, a concept strongly opposed by Islam. In Islam, God is the supreme and all-comprehensive divine name. All other divine names are believed to refer back to The One, God. Allah is unique, the only Deity, creator of the universe and omnipotent. Arab Christians today, having no other word for 'God' than Allah, use terms such as Allāh al-Āb (الله الآب) "God the Father". There are both similarities and differences between the concept of God as portrayed in the Qur'an and the Hebrew Bible. Allah does not have any associate or partner, and He does not beget nor was He begotten.
Unicode has a codepoint reserved for Allāh, ﷲ = U+FDF2. Many Arabic type fonts feature special ligatures for Allah.
The term Allāh is derived from a contraction of the Arabic article al- and "deity, god" to meaning "the [sole] deity, God" (ho theos monos). Cognates of the name "Allāh" exist in other Semitic languages, including Hebrew and Aramaic. The corresponding Aramaic form is אֱלָהָא ˀĔlāhā in Biblical Aramaic and ܐܰܠܳܗܳܐ ˀAlâhâ or ˀĀlōho in Syriac.
In Islam, Allah is the proper name of God, and humble submission to His Will, Divine Ordinances and Commandments is the pivot of the Muslim faith. "He is the only God, creator of the universe, and the judge of humankind." "He is unique (wahid) and inherently one (ahad), all-merciful and omnipotent." The Qur'an insists upon "the reality of Allah, His inaccessible mystery, His various names, and His actions on behalf of His creatures."
According to the tradition of Islam there are 99 Names of God (al-asma al-husna lit. meaning: "The best names") each of which evoke a distinct characteristic of Allah. All these names refer to Allah, the supreme and all-comprehensive divine name. Among the 99 names of God, the most famous and most frequent of these names are "the Merciful" (al-rahman) and "the Compassionate" (al-rahim).
Most Muslims use the untranslated Arabic phrase "insha' Allah" (meaning "God willing") after references to future events. Muslim discursive piety encourages beginning things with the invocation of "bismillah"(meaning "In the name of God").
Muslims are recommended to repeat phrases like "Subhan-Allah" (Holiness be to God), "Alhamdo-Lillah" (Praise be to God), "La-il-la-ha-il-Allah" (There is no deity but God) and "Allah-o-Akbar" (God is great) as a devotional exercise of remembering God (zikr). In a Sufi practice known as zikr Allah (lit. remembrance of God), the Sufi repeats and contemplates on the name Allah or other divine names while controlling his or her breath.
Arab Christians have used two forms of invocations that were affixed to the beginning of their written works. They adopted the Muslim basm-allah, and also created their own Trinitized basm-allah as early as the eight century CE. The Muslim basm-allah reads: "In the name of God, the Compassionate, the Merciful." The Trinitized basm-allah reads: "In the name of Father and the Son and the Holy Spirit, One God." The Syriac, Latin and Greek invocations do not have the words "One God" at the end. This addition was made to emphasize the monotheistic aspect of Trinitian belief and also to make it more palatable to Muslims.
Languages which may not commonly use the term Allah to denote a deity may still contain popular expressions which use the word. For example, because of the centuries long Muslim presence in the Iberian Peninsula, the word ojalá in the Spanish language and oxalá in the Portuguese language exist today, borrowed from Arabic (Arabic: إن شاء الله). This word literally means "God willing" (in the sense of "I hope so").
Some Muslims leave the name "Allāh" untranslated in English. Sometimes this comes from a zeal for the Arabic text of the Qur'an and sometimes with a more or less conscious implication that the God that Jews and Christians worship is not completely true in its details. Conversely, the usage of the term Allah by English speaking non-Muslims in reference to the God in Islam, Marshall G. S. Hodgson says, can imply that Muslims are worshiping a mythical god named 'Allah' rather than God, the creator. This usage is therefore appropriate, Hodgson says, only for those who are prepared to accept its theological implications.
According to Francis Edwards Peters, "The Qur'an insists, Muslims believe, and historians affirm that Muhammad and his followers worship the same God as the Jews (). The Quran's Allah is the same Creator God who covenanted with Abraham". Peters states that the Qur'an portrays Allah as both more powerful and more remote than Yahweh, and as a universal deity, unlike Yahweh who closely follows Israelites. According to the Encyclopædia Britannica:
God, says the Qur'an, “loves those who do good,” and two passages in the Qur'an express a mutual love between God and man, but the Judeo-Christian precept to “love God with all thy heart” is nowhere formulated in Islam. The emphasis is rather on God's inscrutable sovereignty, to which one must abandon oneself. In essence, the “surrender to Allah” (Islam) is the religion itself.
The word Allāh is always written without an alif to spell the ā vowel. This is because the spelling was settled before Arabic spelling started habitually using alif to spell ā. However, in vocalized spelling, a small diacritic alif is added on top of the shaddah to indicate the pronunciation.
One exception may be in the pre-Islamic Zabad inscription, where it ends with an ambiguous sign that may be a lone-standing h with a lengthened start, or may be a non-standard conjoined l-h:-