rdisp/rfc_max_login is a SAP Parameter attribute which is used to control Quota for logins 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 .
Quota for the number of logged-on users on the SAP system. If this value
is exceeded, no further resources are returned to the caller, so that
the server does not become overloaded. The value is given as a
percentage. In other words, it is dependent on the value currently set
in the profile. The parameter
See SAP Parameter Documentation for full SAP documentation for this profile parameter.