Acronym for Graphic (or Graphical) User Interface. This term loosely applies to any system in which control, navigation, or commands are issued through a series of icons, pictures, or other graphic elements that represent specific parts or functions of that system. The purpose is to provide a user interface that is simple and intuitive to use. The most well known example is the Macintosh computer, which was the first commercially available home computing system with a true GUI OS built right in. Nowadays many systems have GUI’s, including some synthesizers and effects processors.