Gallimaufery (pronounced 'gally-maw-fairy') refers to words that are so obscurely defined that nobody knows what they mean. It's like the linguistic equivalent of a participation trophy, but instead of a trophy, you get a confused look on someone's face when you try to use it.
Example: "The term 'gallimaufery' was first coined by someone who was trying to describe a word that defied description, but ended up just describing a word that defied description."
Want to learn more about other words that defy description? Check out our:
Ultracrepidarians page for words that describe nothing in particular, but sound very impressive. Merriam-Websterisms for words that are so obscurely defined that you'll never use them in real life.