I should probably explain what I mean by "dingus."
The dictionary definition gets the broad sense of it. It's an object, that you either can't name or don't want to bother naming. Comes from German. Used in the Maltese Falcon, to refer to the eponymous bird.
I tend to use it more specifically: A dingus is an object, in a story, that the characters in the story want. This, then, drives the plot.
"Object" is maybe not exactly the right word. Because I use it to describe characters. Although, technically, there's usually something else that could be described as the dingus in that sort of situation--like with Jack Sparrow, in Pirates of the Caribbean 2 it's actually his soul that matters. Calling the character the dingus still works, though, because it's a word that describes an element's function in the story.
I picked it up from The Big List of RPG Plots, by S. John Ross. Which is a wicked handy web page, for GMs and writers. And people who want to make fun of GMs and writers for use clichéd plots. (Which every plot is, if you break it down far enough. It's just one of those things they aren't making any more of.)
It's a cool word. It's a way to simplify complex plots, which makes it handy for talking about story in general, and for talking about (and designing) RPG plots in particular.
RPGs really demand simplicity from their plots--or, rather, they demand that the plots have a simple core. There are a lot of reasons for this, but the big one is that the players need to be able to figure out what to do next fairly quickly. If the GM has an understanding of the plot on a very basic level, such that dingus thinking can provide, it's easier to help players figure that out. Being able to analyze the plot simply is useful whenever you're talking about (or designing) any story, but it's particularly vital in an RPG.
Plus, it's fun to say. Which is the real reason why I use it.