Bad wine, or not bad wine
Sometimes bad stuff happens to wine as it travels across the country or the world. Let's take a look at some common 'bad stuff' and their terms.
Corked wine - When a wine that is "corked" is opened you can tell, honest anyone can recognize that can smell. It smells like a wet basement, musty fruit, or rotten cardboard. It happens because the cork itself contaminates the wine with a chemical, TCA. TCA occurs when natural fungi, which cork has comes in contact with certain chlorides during sanitation. Many wineries have for this reason eliminated the use of chlorine based sanitation. Corked wine is not harmful, it just taste awful.
An over-the-hill wine - You can often tell a wine that has aged too long by faded color or a taste that doesn't seem near as good as it should. The cause is often how it has been stored or how long it has been stored. Many wine produced today are not intended to be aged and but to be consumed within a few years. Honestly this becomes a matter of perspective. A wine that has been around a bit longer that it should is often more subtle and is darker color than intended. This may be absolutely perfect for your palate.
Oxidation - Wine that have been exposed to too much air for too long turns to a different color and becomes more brownish, or dark orangish. All wine is unique and some last beautifully for 5 to 6 days, others are done within 3 to 4. Again wine that has been exposed to air too long is often more vinegary in taste and will seem 'off.'