UI vs UX
UI is what the interface is made of. UX is what happens to the person using it. Confusing them produces beautiful products nobody can finish a task in.
Beginner6 min readVanshikaDEFINITIONDesign
UI
User Interface
Everything a person can see and interact with in a product: type, colour, spacing, buttons, icons, and layout.
EXAMPLE
The size of a button, the contrast of a label against its background, and the gap between a field and its heading are all UI decisions.
WHY IT MATTERS
For a first-time visitor it's the only evidence available about care taken everywhere else. Visual carelessness is read as a signal about the parts they can't see.