1. The removal of an oxygen atom from a nitrogen compound (like NO3 to NO2, NO2 to NO, or NO to N2). This is something soil bacteria do successively until they release nitrogen gas, and is the opposite of nitrogen fixation.

  2. The removal of nitrogen or nitrogen compounds from a substance.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.