The term "Postmodernism" refers to a philosophical and cultural movement that are distinguished largely by being different from Modernism. The term is hard to define precisely because it has applications in a diverse number of disciplines, including philosophy, art, architecture, film, television, music, sociology, fashion, technology, literature, and communications. It was first studied academically in the 1980's, but is thought to have originated earlier. Exactly when it originated is difficult to pinpoint, of course, but may have first emerged as a burgeoning movement in the 1960's.
Postmodernism emphasizes the role of individual, rather than standardized or canonical, reaction to and interpretation of our experiences. In art, Postmodernism, like Modernism, does not make strong distinction between low and high forms (as prior art movements had), rejects rigid genre boundaries and favors mixing of ideas, and promotes parody, irony, and playfulness. Unlike Modernism, Postmodern art does not approach this fragmentation as tragic, but rather celebrates it. Modernists desired to unearth universals or the fundamentals of art. Postmodernism resists monolithic universals and encourages fractured, fluid and multiple perspectives. Wikipedia is a good example of a postmodern project.
Postmodernist art may be seen as a reaction to the reductionism and abstraction of Modernism. Andy Warhol is an early example. [eJK]
In economics, Postmodernism refers to multinationalist, consumer-based capitalism, as opposed to monopoly capitalism associated with Modernism through the first half of the 20th century, or market capitalism before that. Some think that the shift in mode and technology of production may have precipitated or at least emphasized the change to Modernism and then to Postmodernism.
There may be many kinds of post-modernisms, since their stance to modernism is the only thing that necessarily unites them. One may define post-modernism similarly as a movement that defines itself in terms of modernism but claims to supersede modernism. Thus, to understand post-modernism you need to understand modernism. In its narrowist sense, the modernism in question is a style of architecture, but you could also include a style of art. "Post-modernism" began as a movement within architecture, that rejected modernist architecture while retaining some of its elements. Classic examples of modern architecture are the Empire State building or the Chrysler building. A classic example of post-modernist architecture is the ATT building in New York, which, like modernist architecture, is a skyscraper relying on steel beams and with lots of windows -- but, unlike modern architecture, it borrows elements from classical (Greek) style. Post-modern buildings are usually not so grand and imposing as modern skyscrapers; they are more playful, and, often through the use of mirrored glass that reflects the sky and surrounding buildings, calls attention to its environment rather than to itself.
Modernism also refers to a style of literature; perhaps Ulysses by Joyce may be the best example, but perhaps anything by Dickens or Tolstoy would serve. One of the most popular post-modern novels is Julian Barnes' Flaubert's Parrot.
One thing that modern art, architecture, and writing have in common is some elevation of an objective and omniscient point of view (think of the role of a narrator in a third-person narrated novel), and a belief in progress. These beliefs have their origin in the Enlightenment (Kant and Compte), so "modernism" can also refer to the enlightenment project in its totality. This is a bit different from structuralism, which was made possible by the enlightenment project but is still something much more specific. For a good study of modernism, see Marshall Berman's "All That is Solid Melts into Air"
Some people think that "modernism" is still a valid project and that we still live in "modernity." The philosopher Habermas is a strong proponent of this view. But some people think that modernity has reached its end; there will be no more progress, just more combinations and re-combinations of what we now have. They feel that the Enlightenment project is bankrupt, that there will be no more progress -- and they celebrate this, they feel that the new global economy, the "information age" has liberated us from everything that the enlightenment sought, unsuccessfully, to liberate us from. These are people who looked to post-modern art and architecture for inspiration in a new philosophy. The leading proponent of this attempt to bring post-modernism into philosophy is Lyotard who wrote a short book called The Postmodern Condition. Guy Debord is another important post-modernist philosopher.
Post-Modernism and Post-Structuralism Although modernism, like structuralism, owes much to the Enlightenment project, they are two different things, so whatever is "post" to each will be different too. Thus, post-modernism is not necessarily isomorphic with post-structuralism, and may not include post-structuralism.
It is perhaps in their respective attitudes towards both the demise of the enlightenment project, and our present circumstances, that one sees most clearly the difference between post-structuralism, which is fundamentally ambivalent, and post-modernism, which is celebratory.
For a light hearted introduction to Postmodernism, I recommend Douglas Adams' series Dirk Gently's Holistic Detective Agency. His better known work The Hitchhiker's Guide To the Galaxy also has many philosophical elements, including Postmodern ideas.
Postmodernism -- In Philosophy (Includes list of postmodernist philosophers)