cross cable

A crossover cable is a cable that is used to interconnect two computers by "crossing over" (reversing) their respective PIN contacts. Either an RS-232C or a telephone jack connection is possible. A crossover cable is sometimes known as a null modem. Possible reasons to connect two computers directly to each other include:
Playing a game competitively (one person at each computer) with fast response time
Testing one computer by examining its behavior at the other computer
Saving the cost of a hub when you want to interconnect two devices in the same home or office