The term Allah (الله) is the Arabic word for God. This theonym is likely a contraction of Arabic Al-'ilāh (ال إِله), which literally translates as "the god" or "The Lord." . It is related to the Hebrew term Eloh(-im) or the Aramaic term "Eloi" which Jesus said on the cross.
In Islam, Allah is the summation of all of the 99 Names of God. When a Muslim refers to Allah, he thinks of God as being One, Creator, Owner, Sustainer, and Almighty, the Most Merciful, the Most Compassionate, and Lord of the Day of Judgement. In Arabic, the name is composed of four letters, ا ل ل ه (or Alif, Lam, Lam, Ha) which when brought together make الله. Arabic speaking Christians and Jews likewise use the term "Allah" as all three religions worship the God of Abraham. Allah is sometimes used incorrectly as a generic word for "god" though the actual generic word for "god" is simply 'ilāh. These Christians do maintain a belief in the traditional Christian Trinity, however, and believe that Allah consists of the Father, Son and Spirit.
Possible Early Use
It is a matter of contention as to whether the name Allah came into use only with the foundation of Islam, or whether it is a reuse of a title of a pagan pre-Islamic Meccan god; Hubal, god of the Moon. Muslim scholars dispute this relationship, though the religious history of the region suggests this is possible..
Takbir (Glorification of God)
Takbir (تَكْبِير) (Glorification of God), is the common way Muslims give glory to God. The wording used is Allahu-Akhbar "الله أكبر", which is translated as "God is great" or "God is greatest." It is a very common practice in Islam and is essential to the Islamic call of prayer (Athan).