What is an icon set you ask? from http://en.wikipedia.org/wiki/Icon_set
A computer icon is a pictogram displayed on a computer screen in order to help user navigate a computer system or mobile device in a similar way traffic signs are used to help a driver navigate traffic; one of the most notable icon designers, Susan Kare was quoted saying "good icons should be more like road signs than illustrations, easily comprehensible, and not cluttered with extraneous detail".Desktop icons for file/data transfer, clock/awaiting, and running a program.
Icons are part of the graphical user interface and belong to the much larger topic of the history of the graphical user interface that has largely supplanted the text-based interface for casual use. The user can activate them using a mouse, pointer, finger, or recently voice commands. Their placement on the screen, also in relation to other icons, may provide further information to the user about their usage. In activating an icon, the user can move directly into and out of the identified function without knowing anything further about the location or requirements of the file or code.