SED stands for the Sozialistische Einheitspartei Deutschlands. It was the official political party of the German Democratic Republic and was originally formed through the union of the East German social democrats and the communist party.
Its role as effectively the only party in East Germany was anchored in the GDR’s constitution.
After the fall of the Berlin wall, the SED was renamed into the SED-PDS and then simply into PDS: Partei der Demokratischen Sozialismus. In 2005 they changed their name to Die Linkspartei, and in 2007 they converged with another party to form Die Linke.
Die Linke have received sufficient votes in some states – even western states – to have seats in local parliaments.
To hear a simple explanation and a short discussion in German, listen to the podcast:
(Press the “play” button to listen to the podcast)