The abbreviation pz stands for pièze, a metric, mts (non-SI) unit of pressure popular in the Soviet Union or perhaps 18th-century France. 1 pz = 1,000 Pa, or 1 kPa.
Which, yes, means this is a completely useless system that is only worth knowing when reading historical documents.
The pièze is defined as 1 sthène per square meter (sn/m^2). (The sthène was the mts unit of force, equal to 1 kN). It works out that 1 pz is 1,000 Pa, or 1 kPa.
Since Pa is already the SI unit of pressure, any applications which were most-conveniently described by pz can now be described by kPa.
This article was a definition of pz. If you are interested in all the different, strange units that are used to measure pressure, I wrote an entire article explaining what each unit is, and how to convert between them. Or, if there is a unit you are especially interested in, you can check out one of the other unit definitions I’ve written.
Other Pressure Measurements:
mbar or bar
psi or ksi