“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.
The other cameras featured in this A to Z Challenge are linked on this page.