Dr. Ravi Zacharias clearly traces the origin and explains the basic tenets of postmodernist philosophy. Postmodernism is philosophical mood that is particularly pervasive in Western culture. Even though as a Christian I do not agree with postmodernism and its relativisation of truth, it has made some useful contributions.
Postmodernism originated from a literary theory that was used by textual critics. Through the avenue of language postmodernist philosophy seeks to break down the structures and institutions that shape human society. Postmodernism is a deconstructionist worldview so it needs to analyse the systems and structures it seeks to tear down. Due to its philosophical and linguistic underpinnings it has unwittingly bequeathed Christians with the tools and terminology to better understand certain things. Things like worldview, metanarrative and figural interpretation are all terms that come from the postmodern framework and help Christians better understand and communicate the Gospel. Personally I have found those terms invaluable in my own studies of the scriptures. Even though as a worldview it does not hold sway over much of the world it is something as believers we need to sit up and pay attention to.