Answer:
Dualism points at dividing in two opposite parts
But the word 'dualism' often points at Western Dualism or Eastern Dualism
Western Dualism (as in Catholicism) divides reality in 'good' and 'evil'.
And supposes 'good' to be an absolute quality (inherent in 'rational' behavior).
And 'evil' is seen as 'irrational' and fought with Wars on Terrorism
In Eastern Dualism (as in Buddhism) 'good' and 'evil' are seen as an ever moving balance (like yin and yang)
Western Dualism produced Industrialism, Capitalism, 2 World Wars, Cold War, Climate Catastrophe. And caused desperate Terrorism and rigid response War on Terrorism.
But is in the Western World seen as a HUGE success...
Western Dualism is the belief that life is made up of a mind and a body. A non-physical 'mind' (soul, spirit, ...) and a physical body. And that the non-physical mind produces 'consciousness'. Western Dualists (in origin Catholics) believe that is this mind/soul/spirit that distinguishes humans from animals and computers.
It's a belief, like in any other religion.