I'm not sure if this is the correct definition, but I think it's an element used by a script that you don't want the user to actually see in the menu. Using a theoretical ABS engine for example (one that hasn't been made, and I don't know if any work like this), say that swords can stab and slash. However, a few big swords can't stab (just because they're freaking huge and it's not plausible to stab with them). So you could add the element "NON-STAB" to every sword you don't want to stab with. But you don't want any menu systems to display that, so you treat it as a dummy element that doesn't get shown to the user.
Or it could just be elements that you're only putting in the editor as dividers to make it easier to keep things organized. (--------Magic Elements--------)