As you may know, wine is sensitive to air. If exposed to too much air, e.g. if a bottle has been opened for a while or if the cork was faulty, the wine goes off and tastes more like vinegar. A more scientific word for air is oxygen and oxidation is a word that describes the process of a wine going off because of the detrimental effect of oxygen.
Although over exposure to oxygen is bad for the wine, exposure per se is not. In fact it can sometimes be beneficial for the wine, but it is obviously something that has to be carefully controlled in the winery.
