User experience (UX) is heavily research-focused. The UX process starts with recognizing problems and understanding the “why” of what is being developed. The target audience is identified, and research is done and hypotheses made in order to determine how to maximize the user’s experience with the product and make it the most enjoyable it can be.
User interface (UI) refers to the technical aspect of design and development—that is, card sorting, flow maps, wireframes, testing, mockups, and prototyping. UI design determines how everything looks and feels and creates the building blocks of a program or application.