gw/max_conn is a SAP Parameter attribute which is used to control Maximum number of active connections 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 specifies the maximum number of simultaneous active
connections. This includes both connections using LU6.2 and connections
using TCP/IP.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.