Lit Terms Applied

When it comes to lit terms, I am somewhat in the middle. I know a good portion of them (such as synesthesia, synecdoche, zeitgeist, rising action and my favorite of all: satire) but there are others (looking at you metonymy, expressionism, postmodernism) that I simply can't wrap my head around. Especially postmodernism. Seems like an excuse for the artistically untalented to claim that their work is actually art and not just scribbles on a piece of paper.