What is it?
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.
UX is important in any medium.
As a scientific process it could be applied to anything, street lamps, cars, Ikea shelving and so on.
What UX designers do:
Strategy and Content
Wireframing and Prototyping
Execution and Analytics