What is an intuitive UI?

A UI is intuitive when it has an appropriate combination of:

*    Affordance: Visually, the UI has clues that indicate what it is going to do. Users don’t have to experiment or deduce the interaction. The affordances are based on real-world experiences or standard UI conventions.
*    Expectation: Functionally, the UI delivers the expected, predictable results, with no surprises. Users don’t have to experiment or deduce the effect. The expectations are based on labels, real-world experiences, or standard UI conventions.
*    Efficiency: The UI enables users to perform an action with a minimum amount of effort. If the intention is clear, the UI delivers the expected results the first time so that users don’t have to repeat the action (perhaps with variations) to get what they want.
*    Responsiveness: The UI gives clear, immediate feedback to indicate that the action is happening, and was either successful or unsuccessful.
*    Forgiveness: If users make a mistake, either the right thing happens anyway or they can fix or undo the action with ease.
*    Explorability: Users can navigate throughout the UI without fear of penalty or unintended consequences, or of getting lost.
*    No frustration: Emotionally, users are satisfied with the interaction.

Of these elements, the first two reflect the dictionary definition, and the others are those extra attributes that go beyond the literal definition.