If you look at some designers' resumes, and then in their portfolios, and then again on the resume, you get the impression that they don't really understand the difference between UI and UX. In fact, this is a common problem not only among designers but also among employers, ranging from small studios to large corporations.
Now we will try to understand the terms and nuances, but before going too far, I want to immediately make some clarity. UI design is quite a "real thing", UX design does not exist.
Therefore, a fashionable combination of UI / UX designer in a resume means only that the designer has not yet figured out the intricacies of his profession.
Now about everything in order.
What is UI
UI - user interface - a tool that allows a person to effectively interact with any product: website, application, software, etc. Moreover, it is important to understand that the interface means not only cosmetic but also a logical component. Many designers prefer to forget about this, shifting the responsibility to the analyst/designer.
Therefore, a thoughtlessly rendered interface is not designed, but shit. No matter how beautiful he was.
To be honest, the very combination of UX design sounds pretty dumb, and now you will understand why.
What is UX
UX is a set of measures aimed at solving a specific user problem. This includes user interface (UI) development, information architecture and strategy creation, usability testing, and a lot, a lot of analytics.
For the most part, designers deal directly with UI. For everything else, there are specially trained people. Testers, analysts, internet marketers and other representatives of the IT industry.
Small clarification. A designer can check the correctness of his judgments only through usability tests and deep analytics. Thus, it can be concluded that UI and UX are inextricably linked. A UI without UX is simply a set of assumptions made by a designer based on their own experience and expertise.