"Interface" has various meanings. Originally Interface means a mechanism to connect things, and to pass around information. For example, Interface between people, between computers and surrounding devices, and so on.

On using PCs, we controll them with a mouse and monitor screen. The information flow from keyboards to monitor have great effect on PC controlling. This interaction between a PC and an user is generally called UserInterface. Hopefully, it's simple enough to contoll. Some periods since PCs have gone out into the world, the UserInterface based on manually input data was popular. Currently, GUI, which is based on window, is popular.

A mechanism called USB and FireWire which interface PCs and surrounding devices. It is required abilities to transfer data as much as possible and simply.