When capitalized, the supreme being of monotheistic religions, including Christianity, Judaism, and Islam.

Also, any powerful being, usually spiritual in nature, which is worshipped by a group of people.

Finally, a person who is possessed of great--nay, insurmountable--power or skill in a given area of expertise; for example, someone can be a guitar god, a hack god, a sex god, or even a barbecue god. Worship is optional, but recommended.