Dualism is a term that refers to any group of thinking where ideas can be separated into two fundamentally different types. For example, this can apply to concepts such as Good and Evil, Existing and non-existing, physical and non-physical. Dualism would be the position that believes in the separate and independent existence of these ideas. On the other hand, monism would believe that no distinction occurs. Often times dualism refers to dualism in philosophy of the mind. In this case, it refers to the dualism between mind and matter (or body). Dualism would assert that these two are separate entities that are not the same. On the other hand, monism would say that there is no difference between mind and matter.
Dualism can be separated into two types typically: substance dualism, and property dualism. The mind-body problem is an excellent example of substance dualism (there are two types of substances, physical and non-physical). Similarly, property dualism purports that there are two types of properties: mental and physical. Physical properties are properties like colour, shape, and size. Mental properties are properties like beliefs, emotions, and passions.