“Your question is simple, the answer a little complicated, and it sometimes can be controversial.
User Experience Design is an approach to design that considers all aspects of a product or service with the user. That includes the beauty and function: (usability and accessibility) of a product or a flow and things like delight and emotion—things that are harder to engineer and achieve.
While a designer can create a toggle, a flow, or an interaction that is beautiful, unique, sexy, and functional in a flow—UXD extends into all the disciplines that come together to make the user experience great.
Yes, you have interaction designers, but you also have content strategists, information architects, user researchers, engineers, and product managers—all of whom have a shared responsibility to create an experience that is easy to use and leaves users pleased because it is adding value to them.”