What is User Interface (UI)?

User interface definition: The user interface is everything a person sees and interacts with in your app — layout, color, typography, buttons, icons, gestures, and micro-animations. If you’re asking what is user interface in the app industry, it’s the visual and interactive layer that turns user intent into action.

How it works

A strong UI reduces cognitive load in the split second after discovery. Visual hierarchy guides the eye; familiar patterns make navigation feel obvious; contrast and spacing make content scannable; motion hints what’s interactive; and feedback (states, haptics, toasts) confirms success.

On mobile, the first screen must earn trust fast: recognizable iconography, clear primary action, and ratings that signal quality. Even small UI tweaks compound — icon clarity, screenshot sequencing, and legible typography can shift how many store impressions become product-page views, and how many views become installs.

Benchmarks show average page-to-install conversion around 25% on the App Storeand 27.3% on Google Play in the US (H1 2024), so the UI that greets users post-click meaningfully influences the final step.

Why it’s important (data you can defend)

Decades of research tie good UI/UX to better business outcomes. Forrester reports well-designed experiences can drive up to 200–400% higher conversion — a directional proof of how presentation accelerates action.

Mobile-specific studies echo the pattern: improving design quality and relevance lifts install propensity, while heavier, clumsier experiences depress it (Google found smaller APKs correlate with higher install conversion).

And because ratings are a public proxy for perceived quality, Apple’s own guidelines emphasize that great overall experience is the fastest path to better reviews — closing the loop between UI polish, reputation, and store performance.

Example

A finance app launches with dense cards, muted contrast, and a floating action button that obscures the balance chart. Reviews mention “hard to read” and “where do I start?” The team widens spacing, raises contrast, promotes a single primary action (“Add account”), and restructures the header to show available balance first.

Within one release cycle, product-page conversion steadies while install conversion rises in the high-20s to low-30s, and average rating climbs as complaint keywords drop — an outcome consistent with category CVR benchmarks and the well-documented link between design clarity and conversion.