It refers to the idea that no internet provider should give preference to certain content -- that means that websites can't pay your internet provider more money for their site to load faster or more reliably than other sites. Net neutrality has faced some major challenges lately, but it's difficult for Americans to stand up for their rights when they don't even know what they're standing up for.
Enter Mark Fiore, political cartoonist and creator of this video that explains net neutrality in the style of a Dr. Seuss book. It might be simple enough for a child to understand, but the message is important enough that it should still scare adults. Free access to information is important. Net neutrality is important. We need to stand up for our rights.