I'm not sure which ads you refer to, but in general, it stands for
Nitros Oxide System. It injects Nitros Oxide into the manifold for
quite a power kick. Really works but is VERY harsh on the engine.

James

>I se the term "NOS" in the description of car parts on eBay and elsewhere.
>
>What means this term??
>
>  R    ���
>  o
>Antaki
>
>  - There's a little Quayle in that Bush...