Monotheism is the belief in one, all-powerful god. Most of the Caprican civilization is polytheistic, but a minority is monotheistic, including a terrorist group known as Soldiers of the One.
Monotheists believe in a more rigid code of ethics or moralities than polytheists - they see the world in shades of "black and white" rather than shades of gray.
The Monotheistic Church is located between two warring factions - the polytheistic rebels on the east and the Hephaestons on the other side. Diego says it is a big stalemate. ("Unvanquished")