stat/adrec is a SAP Parameter attribute which is used to control Max. number of ad statistic records, created for one statistic record 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 .
You can use the parameter stat/adrec to activate the AD statistics
within the SAP statistics. These are used to record the AD opcodes
(administration calls) from the R/3 kernel.
If you activate the AD opcode statistics, the statistics file requires
more space. You can activate/deactivate the AD opcode statistics at
runtime using transaction ST03.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.