The user interface, in the industrial design field of human–machine interaction, is the space where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the machine which aids the operator in making operational decisions. Examples of this broad concept of user interfaces include the interactive aspects of computer operating systems, hand tools, heavy machinery operator controls, and process controls. The design considerations applicable when creating user interfaces are related to or involve such disciplines as ergonomics and psychology.
http://en.wikipedia.org/wiki/User_interface
General interfaces
An interface isn't only restricted to computers and machinery, it can also apply to everyday objects and interactions. For everyday objects, washing machines have an interface that involves buttons and knobs, pepper grinders require twisting in order to sprinkle, and toasters use a sliding button to put the toast in. Pubs are an interface for human interaction and so restaurants or cafes.
