Music Player Command
Music Player Command (MPC) is a console program for controlling the Music Player Daemon audio player. MPC sends commands to control a local or remote running MPD. It allows you to do just about everything the GUI controllers do: Add files to the playlist, play, pause, switch song, etc.
 Why you want MPC
Music Player Daemon is a different way to play music; the daemon (running remote or locally) keeps on playing music regardless of you stopping X11 or shutting down your desktop (if MPD is running on a remote box).
MPC allows you to control the MPD. The most interesting usage for MPC is to assign keyboard shortcuts to run MPC commands. If you have one of those over-bloated "multimedia" keyboards with those big play/stop/forward/back buttons then you can assign Fluxbox or KDE's khotkeys to run mpc play, mpc pause and so on.
MPC may also be a preferred choice for controlling MPD if you view X11 and this whole GUI trend to be a over-rated momentarily passing trend which is bound to go away when enough people realize that the command-line is way more l33t.