UI design (or user interface design) is the design process of a digital interface for applications.
UI design is about how people interact with a computer or software. Today we interact with more screens than ever before. Think about tablets, smartwatches, e-readers, smartphones… The average person spends about 3 hours a day on their smartphone alone. All this makes UI design increasingly important when building modern digital products, as a great interface leads to better conversions and user retention.
User-friendliness: Great UI design creates a better experience, making it more enjoyable for users to work with your (web) application or website.
Branding: When done correctly, your UI helps build and define your brand identity.
Trustworthiness: Ensuring that your UI and branding are in sync with one another creates consistency, which then leads to trustworthiness as users can clearly recognise you and your brand.