Post Modernism is a term applied to a number of trends in Modern Culture as written about by (mostly French) theorists.
The basic premise of their argument is that the apparent 'Evolution/Development' of 'Western Thought' from the Renaissance to the Enlightenment to the Industrial Revolution to the Rational- Scientific - Secular modern world is now at an end - or at least the 'West' is now longer so confident that it has the 'road map to the future' as it was.
It can also be argued that the theories are made up by Marxist Intellectuals mainly to account for:
a) Why Intellectuals aren't taken seriously anymore
b)Why there wasn't a Marxist Revolution in 1968
The theory is not withstanding particularly appropriate to the study of 'Mass' or 'Popular' Culture' and the 'Post Industrial' Consumption & Leisure based economies of 'late capitalism' which so puzzled the Frankfurt School.
An example of this might be the contrast between a 'Modernist' documentary like 'Life on Earth' which 'explained' the natural world using one of the Big Ideas of modernism (Evolution) and 'Big Brother' a 'documentary' without a 'point' to make. The 'modernist' documentary says 'look at the underlying explanation to this diverse world' .The 'post-modern' documentary however seems to say 'look, enjoy,consume, no explanation needed.'
Lyotard, Derrida, Jameson and Foucault are amongst the theorists associated with this position.
The book 'An introduction to theories of popular culture' by Dominic Strinati has a useful chapter on Post Modernism.
Baudrillard is probably the the most readable of the theorists and we will be looking at his ideas about 'hyper-reality' & his criticism of American Culture in detail (The film 'The Matrix' is very much influenced by his ideas)
For web research try the recommended sites - or use 'www.google.com' to find your own (Google is the best Search Engine for finding educational sites)
For a fuller Definition of Post Modernism see the following: Jon Mattox Site