Affordance gap
The mismatch between what an interface can do and what it visibly offers — functionality that exists but is signaled nowhere.
Example usage
“Long-press to reorder is a classic affordance gap — the feature exists, but nothing in the UI admits it.”
Editor’s note
Affordance gaps are where features go to be undiscovered: swipe actions, right-click menus, keyboard shortcuts, double-tap gestures. Power users find them; everyone else lives without them. Either signal the interaction, teach it once, or accept that you shipped it for the demo.