UI is a shortened form of the “user interface”, which is a graphical representation of the app. It consists of everything a user interacts with. For instance,
Anything that is visually seen or interacted with is a part of the UI design. This type of design marks the final look of the application. And, this job is assigned to UI designers.
UX, in its turn, is a “user experience”. It does not represent any visual element. However, it represents the way users interact with the app. Is their experience positive or negative? Is the app logical and a user can navigate it easily or vice versa? Are users resolving their main tasks with the help of the app or it seems impossible?
All of these questions show that UX stands for a particular smoothness of interaction (or the lack of such) and visual satisfaction (or dissatisfaction) that both UI and UX designers have created. UX is sort of a user journey throughout the app. The more users are satisfied with it the better. Thus, UX marks the operational part of the application.
Working together UI and UX designers have one common mission to make the app top-notch for the users. And, while UI designers make the app look attractive, UX designers define how this app will operate and what logic it will have.