"Structuralism" says that we can see human culture as a structure that looks like language. It also says that this is not reality, but we can use a "third order" that makes a bridge between the two. A post-structuralist might say that to build meaning out of that, you have to make a mistake and think that the definitions of things are good and don't change. Post-structualists might also say that the structuralist theory is above and not a part of from these structures they are writing things about.