The word 'Allah' in Arabic simply means "the (al) God (Ilah)." The term is related to Elohim, the Hebrew word for God. There are also the 99 names of Allah that exemplify his majesty and superiority.
It is important to note 'Allah' is not a different God from whom Christians and Jews believe in.
An interesting fact is that Jesus in Aramaic called God 'Alaha' when he referred to Him, very similar to the arabic word for God which is 'Allah'!
In Hebrew, the word for God is 'Alohim', again very similar to the word 'Allah'. Jews refer to God as Yahweh, among other names.
Just because of the language difference, people think Allah, Alaha, and Yahweh are different Gods, but in fact the words in their respective language all the mean and refer to the one and only 'God'.