GSPd is a NMEA-decoder server on Linux (maybe also on Windows). Every GPS client that need geo-location should be connected into this server.
Command-line for GSPd calling is ..
> gpsd /dev/rfcomm0 -D 5 -n -N
It mean that you want to connect with GPS device via bluetooth-serial port to receive NMEA messages: while the other GPS clients need to get an information by request via TCP port into this server.