“Z” is for the Zorki C camera, manufactured by the Russian company Krasnogorsk Mechanical Factory (sometimes abbreviated KMZ).
Zorki cameras are copies of high-end Leica and other cameras. The Zorki C is similar to the Leica II.
The main difference between the Zorki and the Leica was the shape of the rangefinder cover.
Reference: McKeown’s Price Guide to Antique and Classic Cameras, 12th edition, ISBN 0-931838-40-1
The other cameras featured in this A to Z Challenge are linked on this page.