What are the principles of Post Modernism?

The term suffers from an inherent vagueness, which is comically ironic because one of the principles of postmodernism (or pomo), if it can truly be said to have any, is the assiduous denial of fixed meaning or interpretation. So ask five people and you will get five answers, probably conflicting.

Disclaimer in place, postmodernism refers clearly enough to the philosophical and artistic genre or viewpoint that follows, well, modernism. (Clever, huh?) Its attributes are largely up for grabs, but when many people use the term, they often mean our current phase of cultural history. I've also seen it used derisively to describe attitudes of people who stand for nothing and a time when knowledge has diminished value. More specifically, when meaning is destabilized and it's no longer possible to say one knows something because that thing can be endlessly spun and reinterpreted according to a narrative of one's choosing, the foundations of truth and coherence ebb away. Literature is one field of study where pomo rages, and a good example is imposing a feminist reading on a text.

I'm aware of no official groups or organizations, but it's not difficult to find webpages describing pomo in either glowing or damning terms.