interface (idea)

Peaceful coexistence between human beings and machines requires clear communication. The best systems convey information so elegantly that we hardly think about the power they give us—boundaries dissolve and we become one with our technologies.
The interface allows this. Common interfaces include the remote control, the stereo, and the touch-tone keypad of a telephone. You see these interfaces not only on the products they were designed for, but also on things such as computer software which has no "natural" interface of its own.
A good book about interfaces is Interface Culture by Steven Johnson.