UX Design refers to the term User Experience Design, while UI Design stands for User Interface Design.
Both elements are crucial to a product and work closely together.
UX DESIGN :
User experience design (UXD or UED) is the process of enhancing customer satisfaction and loyalty by improving the usability, ease of use, and pleasure provided in the interaction between the customer and the product.
Despite it being an older and more practiced field, the question of “What is user interface design?” is difficult to answer by its ranging variety of misinterpretations.While User Experience is a conglomeration of tasks focused on optimization of a product for effective and enjoyable use; User Interface Design is its compliment, the look and feel, the presentation and interactivity of a product.But like UX, it is easily and often confused by the industries that employ UI Designers. To the extent that different job posts will often refer to the profession as completely different things.