UI/UX Design is the process of improving the user-experience (UX) of a product, application or service.
The UX Designer researches user behaviour, and their interaction with a product or application or service.
This insight influences the design process, and informs the creation or improvement of a product, application or service.
The UX Designer is responsible for understanding user behaviour and needs, and converting those insights into user-experiences (UX).
The UX Designer translates those user-experiences into visuals: with illustrations, icons, navigational designs, colour palettes, typography, etc.