Reduced: Commonly used to describe a wine that has not been exposed to air and has developed stinky aromas due to reductive chemical reactions (as opposed to oxidation). Reduced notes in a wine generally result from the presence of volatile sulfur compounds, or mercaptans; these notes include rotten eggs, rubber, struck matches, sewage and even skunk. These off aromas may dissipate after exposure to air through decanting or swirling the wine in the glass.
Reductive: Refers to winemaking practices that reduce a wine's exposure to oxygen, such as the use of stainless steel tanks and inert gases to minimize contact with air. This is done to maximize a wine's fresh fruit flavors. However, in some cases it can result in "reduced" aromas, considered a flaw.
Oxidized: Describes wine that has been exposed too long to air and taken on a brownish color, losing its freshness and perhaps beginning to smell and taste like Sherry or old apples. Oxidized wines are also called maderized or sherrified.
Oxidative: Refers to winemaking practices that deliberately expose the wine to oxygen, such as the use of open-top fermentors and racking. Traditional winemaking exposes the wine to some air, but does not result in oxidized notes. An aggressively oxidative approach can result in nutty notes, as seen in wines such as Sherry or vin jaunes from the Jura.
Mercaptans: Also known chemically as thiols, mercaptans are organosulfur compounds that emit unpleasant, skunky aromas of rubber, sulfur or garlic. Mercaptans are often encountered in wines suffering from reduction (in which case exposure to oxygen may alleviate the flaw) as well as in very old white wines.