Human-Machine Interface
Formal
A user-interface is consisting of hardware and software that lets a person send requests/commands to a machine. Typically HMIs are meant to make it as easy as possible for a person to control a machine with little difficulty.
Practical
Typically HMIs are meant to make it as easy as possible for a person to control a machine with little difficulty. A great example here would be a smartphone. With a smartphone, a user would perform various actions in order to navigate to the phone-call application and place a call.
