In versions of windows since 95, the system tray is the rightmost portion of the taskbar. It contains a clock, as well as several icons that represent important goings-on in your system. Typical examples would be icons representing the status of your current network connection, an icon representing your current display, and an icon used to control sound volume. Other programs that are designed to do things unobtrusively in the background often put icons here as well. These icons can usually be right clicked, letting you configure various settings associated with the icons.