The two main views in the history of philosophy are MATERIALISM and IDEALISM, the former being the view that matter is primary over mind, and the latter being the vice-versa view. Dualism, however, is the "can't-make-up-my-mind" compromise theory that neither matter nor mind is primary; that both are real, but completely independent. The problem then, of course, is to figure out how these two "completely independent things" can ever interact. How is it, for example, that I can physically raise my arm when my mind decides to do so? Dualists usually try to sweep this embarrassing question under the rug, or else give some totally off-the-wall answer along the lines of DESCARTES, that "somehow" mind and brain connect up in the "pineal gland".
From the point of view of dialectical materialism, dualism is just a variety of idealism, since it is another way of saying that matter is not primary.