As I have recently used this expression I take the chance to answer Simona’s question who, specifically, had a weird experience with a “reduced wine”.
A “reduced wine” is a wine which has not been exposed to oxygen enough developing stinky aromas of gas, sulfur, eggs.
It is the opposite condition of an “oxidized wine” which has been exposed to air changing in colour and developing Sherry-like flavours.
This happens because during the winemaking process oxygen is strictly controlled especially to avoid oxidation but it is crucial to find the proper balance between these 2 extremes.
NB: sometimes, these stinky aromas can disappear making the wine breath a little bit, make a try