UX refers to the user experience. User experience relates to how the user feels when interacting with a product or service. It refers to the ease of interaction and overall usability of the product, rather than what is physically visible.
UI means user interface, which refers specifically to the screens, buttons and other visual and interactive features that people use to interact with digital products such as websites and applications.
UX design is the careful planning and creation of the user experience and everything related to it. UX design focuses on creating a product or service that solves a specific user problem and ensures that the proposed solution is easy and enjoyable to use.
UI design is the process of designing the appearance and behaviour of a digital interface, which includes all the visual and interactive features of a website, software or application, from colours and typography to buttons, scrolling functions and animations.