This statement tells the JES to write the sysout data set to the device handling class Z output.
technically correct, but completely useless to the TS
ususally ... ( by tradition )
sysout=x is for held output ( for TSO users )
sysout=z is a sysout class that gets assigned to a JES dummy writer to just process it without doing anything ( apart deleting it from the spool )
anyway sysout classes are installation dependent, so better ask Your peers or Your support