What is "potsdam-mittelmark"

Potsdam-Mittelmark is a Kreis (district) in the western part of Brandenburg, Germany. Its neighbouring administrative units are (clockwise from the north) the district of Havelland, the free cities of Brandenburg and Potsdam, the state of Berlin, the district of Teltow-Fläming, and the districts of Wittenberg, Anhalt-Bitterfeld and Jerichower Land in Saxony-Anhalt.