In organic chemistry, nitration is a general class of chemical processes for the introduction of a nitro group (?NO2) into an organic compound. The term also is applied incorrectly to the different process of forming nitrate esters (?ONO2) between alcohols and nitric acid (as occurs in the synthesis of nitroglycerin). The difference between the resulting molecular structures of nitro compounds and nitrates (NO?3) is that the nitrogen atom in nitro compounds is directly bonded to a non-oxygen atom (typically carbon or another nitrogen atom), whereas in nitrate esters (also called organic nitrates), the nitrogen is bonded to an oxygen atom that in turn usually is bonded to a carbon atom (nitrito group).

Reference
Wiki: Nitration