Discoverability: Why Can an Existing Function Feel Absent?

Discoverability is not about whether a function works. It asks whether someone who does not yet know the function exists can notice what actions are available. If a phone reveals a photo's location only after an upward swipe, with no clue that the gesture is possible, the feature may work perfectly and still be absent from many people's experience.

This differs from usability, which concerns how easily a task can be completed after the function has been found. It is not identical to visibility either: keeping every option permanently on screen may make each one visible while making the whole interface crowded. Good discoverability supplies cues when they are useful, through button form, a short prompt, feedback on first use or a familiar location.

The idea also applies to institutions and knowledge. A service may formally exist, yet remain hard to discover because its entry point uses language understood only by insiders. Existence does not create access by itself. When action depends on already knowing a secret path, the system has transferred the learning cost to the user.

https://www.nngroup.com/articles/navigation-ia-tests/