That is an acronym for the company, Nitrous Oxide Systems, which is the largest marketer of nitrous oxide injections system for automotive use. Injection of nitrous oxide into the combustion chambers of an internal combustion engine as a way to increase power output was discovered by the German air craft industry early in the Second World War. The British Royal Air Force also used aircraft engines with performance enhanced by nitrous oxide. Interestingly, there was no use of nitrous oxide injection by the American military air forces other than very limited experimental use. Today nitrous oxide injection, like many other modifications such as more aggressive camshafts, bigger carburetors, higher compression ratios, more free flowing intake and exhaust systems, can be a pracitical way to more horsepower.
Nitrous oxide is a colorless, non-flammable gas.
It has a slightly sweet taste and odor. When inhaled in pure form it will cause death by asphyxiation because at atmospheric temperatures and pressure, the oxygen in nitrous oxide is not available to the body. A property of nitrous oxide is that at about 565 degrees F., it breaks down into nitrogen and oxygen. When it is introduced into the intake tract of an internal combustion engine, it is sucked into the combustion chamber and, on the compression stroke, when the charge air temperature reachs 565 deg. If we add extra fuel during nitrous oxide injection, the effect is like a super charger or increasing the compression ratio of the engine.