rsts/filename is a SAP Parameter attribute which is used to control Rule for creation of TemSe directory and filename information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
This parameter contains the rule for generating the TemSe object name in
the file system. This can also be a combination of a directory and file
name (relative path name).
See SAP Parameter Documentation for full SAP documentation for this profile parameter.