Multimedia Keys
Many keyboards include some special keys (also called hotkeys or multimedia keys), which are supposed to execute an application. These keys are known by some different terms such as Multimedia Internet Keyboard Buttons. These keyboards have special keys used to access the Internet, music, and other frequently used programs such as email. A typical example contains buttons that control various computer processes, such as turning on the computer's power, putting the CPU to sleep, and waking it up again.
Multimedia keyboards designed for use with Microsoft Windows typically come already programmed, ready to use right out of the box.
Media Keys Under Linux
In Ubuntu 5.10 (Breezy Badger), Ubuntu 5.04 (Hoary Hedgehog) and later Ubuntu versions, please go to System menu -> Preferences -> Keyboard Shortcuts to find the keyboard shortcut editor. For Kubuntu, see KDEMultimediaKeys. For Xubuntu, see XfceMultimediaKeys.
GNOME directly queries X11 for its media keys support, so you don't need to manually configure it. However, Xfce doesn't, and you'll have to manually get the keycodes and set the symlinks.
Another laternative: Xbindkeys is a program that allows you to launch shell commands with your keyboard or your mouse under X Window. It links commands to keys or mouse buttons, using its configuration file. It does not depend on the window manager and can capture all keyboard keys.