Pluralism is a term used in philosophy, meaning "doctrine of multiplicity", often used in opposition to monism ("doctrine of unity") and dualism ("doctrine of duality"). The term has different meanings in metaphysics, ontology, and epistemology.
In metaphysics, pluralism is a doctrine that there is more than one reality, while realism holds that there is but one reality, that may have single objective ontology or plural ontology. In one form, it is a doctrine that many substances exist, in contrast with monism which holds existence to be a single substance, often either matter (materialism) or mind (idealism), and dualism believes two substances, such as matter and mind, to be necessary.
In ontology, pluralism refers to different ways, kinds, or modes of being. For example, a topic in ontological pluralism is the comparison of the modes of existence of things like 'humans' and 'cars' with things like 'numbers' and some other concepts as they are used in science.
In epistemology, pluralism is the position that there is not one consistent means of approaching truths about the world, but rather many. Often this is associated with pragmatism, or conceptual, contextual, or cultural relativism.