Out of my experience,
S7-Verbindung (S7-Connection) is a closed SIEMENS protocol, used to communicate all its equipment (PLCs, PC-stations, HMIs, ...), using "Total Automation" concept.
Physically, it may be any interface (MPI, PROFIBUS, Ethernet).
Example of simple S7-connection without S7-routing:
Example of simple S7-connection with S7-routing (PC to CPU315-2DP):
To use S7-routing feature all connections must be programmed in NetPro