The user interface (UI), in the industrial design field of human–machine interaction, is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine from the human end, whilst the machine simultaneously feeds back information that aids the operators' decision-making process.
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.
Mobile first design is an approach outlined in 2009 by Luke Wroblewski. Put simply, mobile first is an approach to responsive design: design for smaller screens first, then add more features and content for bigger and bigger screens. This design approach is also known as "progressive enhancement."