A kind of electrical connection using two wires, one of which carries the normal signal (V) and the other carries an inverted version the signal (-V). A differential amplifier at the receiver subtracts the inverted signal from the normal signal to yield a signal proportional to V. This subtraction is intended to cancel out any noise induced in the wires, on the assmption that the same level of noise will have been induced in both wires. Twisted pair wiring is often used to try to ensure that this is the case.
The two wires might be connected at the receiver to separate analogue to digital converters and the subtraction performed digitally.
The RS-422 serial line standard specifies differential drivers and receivers, whereas the earlier RS-232 standard does not.
Opposite: single ended.