rdisp/tm_max_no is a SAP Parameter attribute which is used to control Maximum number of entries in tm_adm 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 restricts the maximum number of logons per instance. This
includes SAP GUI logons, RFC and HTTP logons, and also logons for
internal tasks (for example, the execution of background jobs or
updates).
See SAP Parameter Documentation for full SAP documentation for this profile parameter.