A wine's vintage refers to which year the grapes were picked.
Most still wines come from a single vintage (wine from the same harvest), and the labels on the bottles should show the year in which this happened. Some lower quality wines or branded ones might not show this.
Non-Vintage wines might be fortified; also sparkling wines, including champagne. This is because they are frequently created from a blend of different vintages, with the aim of creating a consistent ‘house style’. The exception to this rule is if a wine was made in a particularly exceptional year.
It is normally the producer who decides whether a year is sufficiently good to produce a single vintage wine. This is done after it passes the assessment period. Port for example is matured in oak barrels for two years before it is assessed before the decision is made and vintage declared.
The difference between vintages lies in the variances of micro-climate of any particular wine-growing region. Different grape varieties respond to different climatic conditions in their own way. For example Syrah/Shiraz responds particularly well to dry, sunny conditions that favour the ripening of its sugars, a key ingredient of its heady, alcoholic kick – that’s why growers in South Australia’s Barossa Valley have been particularly successful in producing wines made from this grape. On the other hand, Sauvignon Blanc responds well to somewhat cooler, damper conditions, which is why it thrives in the Loire Valley and New Zealand’s South Island.
Another example of this is the 2011 Italian Amarone vintage, while the producers of other wines struggled to produce equally good wine that year due to climate variations, for the Amarone these variations were optimal to create one of the best vintages up to that point.
So remember, because a year was good for a particular wine, it does not mean it was an equally good vintage for all other wines.