[pastpeak]

People often talk about compounds being oxidized or reduced. E.g., nitrite is oxidized to give nitrate. Or NAD+ is reduced to give NADH. But oxidation state applies to specific atoms within compounds, not to compounds as a whole. Is this just sloppy usage? Or are there some rules or heuristics that apply to such statements that make their meaning clear and unambiguous?

[Borek]

Oxidation state (or oxidation number) doesn't have - especially in compounds - any related property that can be measured. Quite often we just assign oxidation state to central atom to make description easier, but it has nothing to do with reality. So it is perfectly correct to say that MnO₄^- got reduced to MnO₄^2-.