Allah
As a proper noun, "Allah" is a name for one God, the god of the Abrahamic religions. In Arabic, the word al is an article (a word for "the"), so al-ILaah means "The God". Usually, the word "Allah" is used by Muslims. However, Arab Christians also call their God "Allah." The name "Allah" is made of four letters in Arabic,  (or Alif Lam Lam Ha, from right to left, A-L-L-H, 2111), which when brought together make الله