(Formerly "Saturnic Navigation", after saturn.com) "Mystery meat navigation" is a term coined by Vincent Flanders, the man behind Web Pages That Suck.
The term means this trend of making pages whose navigation is based more or less on guessing. People make "artistic" navigation bars and such that have cool images that tell nothing of where the links will lead.
This was one of the great design "trends" a while back, but fortunately it has not caught on in recent times. Apparently people will notice sooner or later that you can't navigate a website if you can't see where you're going.
The best and most famous parodying illustration of the problem, from the original article: Imagine if road signs on highways would be empty, and the text and symbols would appear on them when you get close enough... Another good example was given as what if amazon.com looked like this?... with blurred tabs that come in focus when you move mouse over them. Good illustrations on why this kind of navigation doesn't work.
For more information: http://fixingyourwebsite.com/mysterymeat.html