A hydrazone is the functional group with structure R1R2C=NNH2. They are like aldehydes or ketones, with an NNH2 group instead of the oxygen atom.
They are made by reacting hydrazines with ketones or aldehydes:
Hydrazones are very useful molecules to do some reactions. For example, a ketone can be reduced down completely if made into a hydrazine and then treated with sodium ethoxide (Wolff–Kishner reduction). Hydrazones are very important intermediates in many reactions, such as the Fischer indole synthesis. This makes indoles, groups which are found in many drugs.