Manicheanism colloquially (in places where it is used colloquially, which may not be all that many) means seeing things in stark black and white - which is not how the world is.

The basic historic Manichean doctrine is that there is a principle of good (call it God) and a principle of evil (call it the Devil), and they are equal and equally eternal. But it's not got all that much to do with the way the term tends to be used.