The ControlPanel is an area which has links to various tools for administering parts of your system. Under Windows95 and its descendants, these include things like display settings (resolution, refresh rate, background, screen saver..), passwords, Internet settings, keyboard and mouse settings and so on.
A similar concept was introduced to GNOME and KDE. A lot of the stuff you can change requires root access, so the better implementations prompt for the root password first.
One page links to ControlPanel:
