It is always a way of living.. The term Hindu was coined to represent the religion only by the british.. So if you Pray Allah or Christ and still follow the Hindu way of living, you will be called as Hindu..Or you can invent your own god or you may not believe in God, but follow the hindu way of living still you will be called as Hindu.. That way Hinduism is a beautiful religion. Thats why many Hindus Visit Mary Temples and Nagore Darkahs..