We live in a post modern society. This is largely because of technology and social media. Today, it is so easy to lie or make something up on social media, that you can never really tell what the "truth" is. Post modernism explores this idea that people's perception of what the truth is can be so easily altered. A very good example of this is Magritte's "This Is Not a Pipe."
This piece makes you reconsider what the truth is. Is the object that we associate with the word pipe really a pipe? This piece seems so simple at first glance, but when you stop to really think about it, it poses a very existential question. I think this is essentially what post modernism is.