1.A surface forming a common boundary between two things, especially between two fluids.
2.(Computers) Hardware that links one device with another (especially a computer).
3.(Computers) That part of a computer program which controls the way a program interacts with a user; the manner of inputting and outputting of data, and the way information is presented on a computer monitor; also called user interface; as, a graphical user interface; a character-based interface.
