Pair trading* is a technique to improve the productivity and quality of stock trading (or any type of financial trading, e.g. commodities). In pair trading, two traders share a single workstation. The trader at the keyboard (usually called the driver) actively trades, while the second trader (called the observer or navigator) is reviewing, advising, thinking through problems and generally sanity checking the first. These two roles switch on a regular basis (e.g. every ½ hour). The pairs also swap partners every day.
*Not to be confused with a Pair Trade