What is "schleswig-holstein-sonderburg-plon"

The Duchy of Schleswig-Holstein-Sonderburg-Plön , also Schleswig-Holstein-Plön, Holstein-Plön or just Duchy of Plön, was a small sub-duchy (Teilherzogtum) created by the physical division of the Duchy of Schleswig-Holstein-Sonderburg. Today, its remaining significance is primarily the building of Plön Castle. The Duchy of Plön was not a territorial dukedom in its own right, but a sub-division within the state structure of the duchies of Schleswig and Holstein. The scattered territorial dominion lay mostly in the southeast part of present-day German state of Schleswig-Holstein.