Slide2-4 User Interface and User Experience Design

UI is the saddle, the stirrups, and the reins. UX is the feeling you get being able to ride the horse.
Dain Miller, Web Developer

It is important to understand that User Interface (UI) Design and User Experience (UX) Design do go hand-in-hand; you cannot have one without the other.
The main difference is that the UX Design is all about the overall feel of the experience, while UI Design is all about the product interface functionality.