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.