Calibre 9mm PAK or P.A.K

The most accepted definition for the acronym PAK or P.A.K is the following :

"PAK is derived from the normal '9mm PA' sometimes used to indicate 9mm Parabellum with the addition of the the K to indicate Knall, which as students of German will know means 'bang' and denotes that it is a blank calibre"

Citation : http://www.agria.hu/(english)/acreklam/mfs/szabaly/2.html
"Simple construction and reliability are the characteristics that make the 9 mm PA. Knall cartridge popular."

Citation : http://mselect.free.fr/glossaries/denominations15.htm
"Dénominations : 9 mm/.380 Knall - 9 mm Knall - .380 Knall - (9 x 17 R)