Differential signaling is a newer and more reliable method of transmitting digital data. Odds are, you've got a device that utilizes differential signaling staring you in the face right now.
For normal digital data transmission, a single wire is used, across which a pulse of either 0 volts or +5 volts is sent to represent data. These are the "zeroes and ones" commonly referred to as binary. (Yes, newer applications like cellphones and laptops use +3.3V. Don't bother correcting me.) The most common problem in digital applications is noise on the line. This noise appears in the form of tiny spikes of voltage that, while very brief compared to a purposeully sent signal, can still register as a high pulse.
The way that differential signaling corrects these anomalies is rather simple. Instead of using only one line as the signal carrier, two lines are used. On onle line is the original data stream, on the other is the complement (inverse) of that data stream. As long as they remain perfect opposites of each other, the data is read and interpreted normally. If there is a small voltage spike, it raises both streams high. Since they are not opposites any longer, the data is ignored until normal function is resumed.