ZSU in original Russian transcription means "Zenitnaya Samohodnaya Ustanovka", or Self-propelled AA mount.
In this guise, the smallest caliber was 23mm (the famous ZSU-23 with quad 23mm cannons), and with bigger twin systems in 37mm and 57mm, all on tracked chassis
The 14.5mm mounts, single, twin and quad, were known as ZU ("Zenitnaya Ustanovka" - AA mount). The variations of ZU theme were made in USSR, Poland, China and probably some other countries - all were based on the same KPV Vladimirov 14.5mm heavy machine gun (except the most recent Chinese ones, which are built on domestic designs).
