What the hell is post-modernism?! Good question, and I bravely attempt to answer it.. more on http://www.unboringlearning.com
The explanation on post-modernism in the above video sits well with me as I have come to see this as a response to deconstruct well-established norms and ideologies that have been formulated in the so-called modern era of the 19th and 20th centuries due to advancements made in science, technology, architecture as well as developments in art, music and literature. So I suppose by the 20th century many textbooks have been written to impart these theories to students in schools, colleges and universities. While this may serve the purpose to pass down valuable knowledge, the downside of such institutionalisation and formalisation of theories and concepts is that a number of people began to accept them as the norms or objective truths when actually these originated only as opinions that were widely accepted as valid.
So I think that is where post-modernism comes into the picture around late 20th century onwards, to reflect and critique well-established ideologies so that people can continue to think for themselves and question popular theories in order to see things from diverse viewpoints. It is relevant and important today because certain norms may have resulted inadvertently in stereotyping and discrimination, such as gender boundaries, social classes, power structures, and so on, as pointed out in the video. I think post-modernism keeps the evolution of human consciousness alive, and encourages people to think for themselves and find new and better ways to look at things and solve problems of inequality, discrimination and so on in the world.