from
The Free On-line Dictionary of Computing (8 July 2008)
null modem
<communications, hardware> A cable, especially an {EIA-232}
cable, for connecting serial ports on two computers directly,
rather than via modems. Since, according to the
specification, both computers should transmit on pin three of
their EIA-232 connectors and receive on pin two, a null modem
cable needs to connect one computer's pin two to the other's
pin three and vice versa. It also needs to have male
connectors at both ends (again, according to the
specification).
(1996-05-17)