Define User Interface Design (UID). 

Definition of Modern Interface Design 

• User interface design is a subset of a field of study called human-computer 
  interaction (HCI). Human-computer interaction is the study, planning, and design of how people and computers work together so that a person’s needs are satisfied in the most effective way.
• The user interface is the part of a computer and its software that people can see, hear, touch, talk to, or otherwise understand or direct. The user interface has essentially two components: input and output.
• Input is how people communicate his needs to the system using keyboard or any pointing device and output is how the system returns processing result to user 
  through screen or sound.
• The best interface is one which has proper design with combination of effective input and output mechanisms.