from Dictionary.com: ersatz \AIR-sahts; UR-sats\, adjective:
Being a substitute or imitation, usually an inferior one. Ersatz derives from German Ersatz, "a substitute."
The term was often used by German soldiers to name the coffee substitute (usually Chichory) that they were provided with as part of their meal ration -ie, erstaz coffee. (imitation coffee).
As M1 says, the Ersatz Panther was a modified SdKfz 171 Panther Ausf G; field modified with sheet steel to make the outline look like an US M10 Tank Destroyer from a reasonable distance.
FrostyGirl scratchbuilt one in 1/72nd scale for the Sherman Group build if you want to go back a few dozen pages to find it. Also Dragon have indicated that they will produce a 1/35th scale kit this year.