login/disable_multi_gui_login is a SAP Parameter attribute which is used to control disable multiple sapgui logons (for same SAP account) 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 .
If this parameter is set to value 1, multiple dialog logons (in the same
client and under the same user name) are blocked by the system: When the
system recognizes a multiple logon, it displays a dialog box with the
options "Terminate the current sessions" or "Terminate this logon".
This parameter works with SAP GUI logons. System logons using remote
function call (RFC) are controlled using the parameter login/di
sable_multi_rfc_login. Logons with SERVICE user master records are also
not subject to the multiple logons check.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.