What is postmodernism?

Postmodernism is the belief that direction, evolution and progression have ended in social history, and society is based instead upon the decline of absolute truths, and the rise of relativity. To me this means that for every positive action there is inevitablly a negative or adverse reaction and therefore postive progress in it's purest form has ceased. For example, progress can be considered curing illness and disease, but a drawback to this progress is overpopulation and all of the negative ramifications that come along with it.