According to the [KDE website]; "KDE is a network transparent contemporary desktop environment for UNIX workstations. KDE seeks to fill the need for an easy to use desktop for Unix workstations, similar to the desktop environments found under MacOS or Microsoft Windows."
KDE was originally patterned after (and presumably intended to replace) CDE, the "Common Desktop Environment". CDE is an older Unix desktop environment used by commercial Unix vendors, such as Sun Microsystems and Hewlett-Packard.
An ongoing flame war has occurred between users of KDE and GNOME as to which GUI is "better". Like most flame wars, there has been little resolution.