KZ

Etymology
The expected initialism was used officially at least in the earlier years of the National Socialist concentration camps. While it is not entirely clear how the informal variant originated, it is usually thought that it came to be preferred and eventually standardised due to its sounding harsher. A possible origin is from the fact that the common German pronunciation of contains the cluster, predominantly represented in German by the letter Z, three times:. Another theory derives it from, which at least officially, however, was never used for the camps.