Pluralism: a theory that there are more than one or more than two kinds of ultimate reality: a theory that reality is composed of a plurality of entities
also: a state of society in which members of diverse ethnic, racial, religious, or social groups maintain an autonomous participation in and development of their traditional culture or special interest within the confines of a common civilization b : a concept, doctrine, or policy advocating this state (Merriam-Webster Online)

OED: A theory or system of thought which recognizes more than one ultimate principle: opposed to MONISM. Also, the theory that the knowable world is made up of a plurality of interacting things.