An icon, when talked about in computing, is a picture which usually stands for a computer program, computer file, folder, or an action for a program to do. Icons are usually small pictures, but not always. Sometimes the user can change what size an icon is.
Icons are used in many places on a computer. The desktop contains icons as shortcuts - clicking on these icons opens up the file, folder, or application that they stand for. For example, in Microsoft Windows the desktop will often have an icon for the Recycle Bin, and the icon usually looks like a trash can in the dextstop.
Shortcut icons also show up in other places such as folders and the start menu. These icons work the same as on the desktop.
Many computer programs use icons on buttons. When the user clicks on the button, something happens. For example, a button with an icon of a printer will usually help the user print what is currently open. While a button with a magnifying glass will let the user search for something.