We’re all familiar with similes and metaphors, right? These can be great ways to infuse your writing with some punch and visual pizzazz. However, sometimes in the process of getting that metaphor written down, something happens, and the plane that was supposed to quickly and efficiently connect the object of your description and your metaphor ends up going all Oceanic Flight 815 on you and crashes somewhere on a remote island where weird things happen and you’re trying to get rescued, but have also kind of resigned yourself to the fact that you’re way off course and no one will be looking for you.
In other words, the last part of the previous paragraph is something you generally don’t want to do. I’m not aware of a specific literary term for a rambling or forgotten metaphor, but you generally want to avoid them.