Vintage, in wine-making, is the process of picking grapes and creating the finished product.
A vintage wine is one made from grapes that were all, or primarily, grown in a single specified year. In certain wines it can denote quality, as in Port, where Port houses make and declare "vintage" Port in their best years. From this tradition, a common, though incorrect, usage applies the term to any wine that is perceived to be particularly old or of a particularly high quality.
Most countries allow a vintage wine to include a portion of wine that is not from the year denoted on the label. Australia, New Zealand and the member states of the European Union require 85% same-year content for vintage-dated wine. In Chile and South Africa, the requirement is only 75%. In the United States, the requirement is 85%, unless the wine is designated with an AVA, (e.g., Russian River Valley), in which case it is 95%. Technically, the 85% rule in the United States applies equally to foreign imports, but there are obvious challenges in enforcing the regulation.
The opposite of a vintage wine is a nonvintage wine, which is usually a blend from the produce of two or more years. This is a common practice for winemakers seeking a consistent style of wine, year on year.