It was only in the decades after the war that the abbreviation KZ (for Konzentrationslager) began to be used in reference to the concentration camps. Before 1945, the abbreviation KL was used in the camps and for administrative purposes. This is why KL is found on documents produced during the war or in the early postwar period. The archive department for concentration camp documents at the ITS was referred to as the KL Department until 2013. For this reason, KL is also found on the individual document envelopes.