service/hostname is a SAP Parameter attribute which is used to control Bind specific hostname or IP address for http/https webservice ports 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 .
Host name or IP address to which the start service is to bind its HTTP
and HTTPS port. Normally all IP addresses (0.0.0.0) are bound. However,
if the Web service interface is only to be accessible using a particular
IP address, you can specify it here.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.