UX Glossary · U
User interface
Also: UI
The surface through which a person operates a system: what they see, hear and manipulate.
The user interface is the point of contact between person and system: screens, controls, type, colour, sound, and physical inputs where they exist.
UI and UX
The two are routinely conflated and are not the same. The interface is the surface; the experience is the whole response, most of which is produced by things other than the surface.
A useful way to hold the distinction: you can redesign the interface without changing the experience at all, if the underlying process, speed and structure stay the same. This is why so many redesigns disappoint.
What UI work actually covers
Visual hierarchy, so the eye lands in the right order. Typography, which is most of what is on screen. Colour, including its use as a carrier of meaning and its accessibility. Layout and density. The component set and its states, which is where a design system comes in.
Every control has more states than the default: hover, focus, active, disabled, loading, error, empty. Designing only the default is the most common source of an interface that looks finished and behaves unfinished.
In practice
The measure of a good interface is not that it is admired. It is that people can predict what will happen before they act, and are right.