SAPFQDN is a SAP Parameter attribute which is used to control Provides the fully qualified domain name (FQDN). 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 .
The full domain name for a specific computer or host in the Internet is
called the fully qualified domain name. The fully qualified domain name
consists of two parts: the host name and the domain name. The host name
is provided by the parameter
See SAP Parameter Documentation for full SAP documentation for this profile parameter.