Returns the name of the computer on which this invocation is being executed. Note that this name is not guaranteed to be the fully qualified domain name of the host. Where machines have several different names (as is common on systems with both TCP/IP (DNS) and NetBIOS-based networking installed,) it is the name that is suitable for TCP/IP networking that is returned.
Basically, what is returned is a string that represents the name of the local computer.
The actual function used can vary, depending on the OS and configuration. On Unix, it might be uname() or gethostname() that is used to obtain the value.