An icon is a small graphical representation of a file, folder, or application. Icons provide a way to interact with something on your computer by first selecting its icon and then issuing a command — deleting a file, moving one to another folder, or double-clicking one to open it. Icons are a fundamental part of computers with graphical user interfaces (GUIs).
The first popular, mass-market computer to use icons to represent files, folders, and applications was the Apple Macintosh in 1984. Older computers relied on a command line interface to issue commands; if you wanted to move a file, you had to type the move command, the file name, and the destination folder. The combination of icons and the mouse allowed users to interact with files directly — to move a file from the desktop into a folder, all you had to do was click the icon representing the file, then drag it onto the icon representing the destination folder.
Icons appear all over the user interface for most operating systems. Applications appear represented by their icons on the macOS dock, the Windows taskbar, and the home screens of iOS and Android devices. Smaller icons in the Windows system tray and the macOS menu bar provide quick access to utility applications. Many file icons even show a small preview of the file's contents — some text file icons show a thumbnail of the text, while some image file icons show a small thumbnail of the image itself.