gw/compatibility is a SAP Parameter attribute which is used to control Compatible to version older than 3.0 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 determines whether the gateway can communicate with SAP
servers older than Release 3.0. For purely 3.0 installations this
parameter should be set to 0. In this case, errors that occurs during
connection setup can be returned to the caller directly without trying
the old procedure again. In mixed installations, this parameter must
have the value 1.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.