Any salt or ester of nitrous acid (HNO₂). The salts are inorganic compounds with ionic bonds, containing the nitrite ion (NO₂⁻) and any cation. The esters are organic compounds with covalent bonds, having the structure RsinglehorzbondOsinglehorzbondNsinglehorzbondO, in which R represents a carbon-containing combining group and the bonding is from carbon to oxygen. These covalent nitrites are constitutional isomers (see isomerism) of the nitro compounds, nitric acid derivatives (RsinglehorzbondNO₂), in which the bonding is from carbon to nitrogen. Nitrites are used as food preservatives and color enhancers, though they are so toxic they have caused deaths and combine with amines to produce carcinogens. They are used in medicine to dilate blood vessels.

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