So we are all using the same terminology: User Interface Design or UI Design, is the visual representation and functionality of a product and the users traversal.
User Experience Design or UX Design, is the application of design so a user's time with a product is maximised and aligned with the products goals.
These two are complimentary, though often times confused with one another. Both are user focused, require relevant time, effort and research.
UI design often culminates with mockups, ui kits and/or handoff specs. UX Design involves interviews, research, testing and analysis so documented evidence might be the only thing presented (though lo-fi wireframes, flow diagrams and personas illustrations can be part of the deliverables).