A User Interface is the visual and interactive layer of a software product that humans interact with. UI encompasses layout, typography, color, iconography, interaction patterns, responsiveness to input, and error presentation. It is distinct from User Experience (UX), which refers to the broader felt experience of using a product, of which the UI is one component.
The modern web UI landscape is dominated by JavaScript frameworks (React, Vue, Svelte), component libraries (Material, shadcn/ui, Chakra), and design systems that encode a product's visual conventions. Mobile UI is dominated by native iOS (SwiftUI, UIKit) and Android (Jetpack Compose, Views) frameworks, with cross-platform alternatives (Flutter, React Native) competing on specific use cases.
AI has entered UI both as a design tool (AI-augmented design assistants) and as a new interaction paradigm. Chat interfaces, voice interfaces, and increasingly agent-driven UIs are reshaping what "user interface" means. The long-term question is whether traditional direct-manipulation UIs coexist with AI-mediated interfaces or are progressively absorbed by them.