An example of interface is someone using the controls on a washing machine to tell the machine how to function.
Public relations firms often serve as the interface between a company and the press.
If water and oil are mixed together, they tend to separate, and at equilibrium they are in different strata with an oil-water interface in between.
The surface of a lake is a water-air interface.
The data is sent over the air interface to the remote system.
The options are selected via the user interface.