Unless you've managed to somehow filter out everything about US politics over the last few months (and if you have, please let me know your secret), then you've likely heard about "fake news". From a high level, my basic understanding of "fake news" is that it refers to stories or websites that are fabricated to advance the political beliefs and/or ideologies of one site or the other. Your definition may differ.
So what is fake code? That, I can at least try to explain in a bit more detail.