[The Captain]

I suppose that he means you'd only be able to make one that connects to the serial port of your PC aka the huge, long port that used to be use by old printers without USB connection. That's my guess.

I'm not sure what he meant, but parallel ports and serial ports are different. Parallel ports are the long ports that used to be used by printers. Serial ports are smaller (about the size of a vga port, but with a different number of pins), but they have become eclipsed by usb and firewire. Serial ports can serve a number of purposes. For example, my old joystick used a serial port.