As wine ages, it oxidizes. Just like iron rusts, oxygen converts certain compounds in wine into other, generally less desirable compounds. At a slow controlled rate this creates the complexity of aged wines. When a wine is too old, or has been exposed to too much oxygen either through a faulty closure or too much time in barrel, the aromas and flavors of an oxidized wine tend to recall toasted nuts, brown spices, and other tan flavors.
Oxidized wine is often referred to as Maderized. Madeira is a famous wine that undergoes an intentionally oxidative winemaking process, giving it a unique flavor profile and the ability to age nearly forever.