Postmodernism as defined by Wikipedia

Postmodernism literally means 'after the modernist movement'. While "modern" itself refers to something "related to the present", the movement of modernism and the following reaction of postmodernism are defined by a set of perspectives. It is used in critical theory to refer to a point of departure for works of literature, drama, architecture, and design, as well as in marketing and business and the interpretation of history, law and culture in the late 20th century.
Postmodernism is an aesthetic, literary, political or social philosophy, which was the basis of the attempt to describe a condition, or a state of being, or something concerned with changes to institutions and conditions (as in Giddens, 1990) as postmodernity. In other words, postmodernism is the "cultural and intellectual phenomenon", especially since the 1920s' new movements in the arts, while postmodernity focuses on social and political outworkings and innovations globally, especially since the 1960s in the West.
The term postmodern is described by Merriam-Webster as meaning either of, relating to, or being an era after a modern one or of, relating to, or being any of various movements in reaction to modernism that are typically characterized by a return to traditional materials and forms (as in architecture) or by ironic self-reference and absurdity (as in literature), or finally of, relating to, or being a theory that involves a radical reappraisal of modern assumptions about culture, identity, history, or language.[1]
The American Heritage Dictionary describes the meaning of the same term as Of or relating to art, architecture, or literature that reacts against earlier modernist principles, as by reintroducing traditional or classical elements of style or by carrying modernist styles or practices to extremes: “It [a roadhouse]is so architecturally interesting . . . with its postmodern wooden booths and sculptural clock” (Ruth Reichl, Cook's November 1989).[2]