The "Lock" menu item lets you lock the applet into its position on the Panel.  Once an applet is Locked, it cannot be moved accidentally.  The "Move" menu item (discussed next) will be "greyed" and you will no longer be able to select it.  To move the applet again, you must first unlock the applet by selecting the "Lock" menu item again.  The "Move" menu item will once again be selectable.
