The word Allah has been used by Arabic people of different religions since pre-Islamic times. More specifically, it has been used as a term for God by Muslims (both Arab and non-Arab) and Arab Christians.
It is also often, albeit not exclusively, used in this way by Bábists, Bahá'ís, Mandaeans, Indonesian and Maltese Christians, and Mizrahi Jews. Similar usage by Christians and Sikhs in West Malaysia has recently led to political and legal controversies.
Allah is never represented by a symbol, but is spelled in Arabic like so:
The Arabic components that build up the word "Allah":