Nitrogen oxide
Nitrogen has six different oxides:
The term nitrogen oxide is imprecise and can be used to refer to any of these or to a mixture of them. A mixture is often formed in chemical reactions that produce nitrogen oxides, with the proportions depending on the specific reaction and the conditions it is performed in. This is one reason why home production of N2O is undesirable; the other two stable oxides - which are extremely toxic - are liable to be produced.
Note that the last 3 listed above are unstable.
See the articles for these oxides for details on their properties, as well as NOx.
