http://en.wikipedia.org/wiki/User_interface
The term user interface is often used in the context of computer systems and electronic devices. The user interface of a mechanical system, a vehicle or an industrial installation is sometimes referred to as the human-machine interface (HMI).
HMI is a modification of the original term MMI (Man-Machine Interface). In practice, the abbreviation "MMI" is still frequently used although some who still use the term may claim that MMI stands for something different now (e.g. "Management and Manufacturing Information" or "Mammal-Machine Interface"), in order to avoid controversy.