The term nitrite (NO2-) is used for the compound nitrogen dioxide (NO2) when singly ionized (one extra electron). NO2 is a compound with molecules each consisting of one nitrogen and two oxygen atoms.
The term nitrite is also used to indicate a compound that includes the ion, presumably with an ionic bond, resulting in a nitrite salt. Examples include or sodium or potassium atom(s).
The presence of nitrite ions is indicated by the spectra of some astrophysical objects and some nitrite compounds may be biosignatures.