Allah is the personal name used only for one true God, who doesn't has
any gender and nothing else can be called Allah. He is similar to
nothing and nothing is comparable to Him as the Holy Qur'an says:
"La'isa
Ka Mislihi Shai'un
Wa
Hu'was Sami-ul Basir."
"There
is nothing like a likeness of Him,
And
He is the Hearing and the Seeing."
Allah is the
Creator and Sustainer of the universe and has no partner in His Kingdom.
When people asked Prophet MuhammadPbuh about Allah, the
answer came from the Almighty Himself in the form of a chapter of Holy
Qur'an, which is considered as the essence of monotheism.
"In
the name of Allah, the Merciful, the Compassionate,
Say
(O Muhammad) He is God the one God, the Everlasting Refuge,