"Vintage" refers to the year the grapes used to make the wine were harvested. It is important to note that this does not refer to the year the wine was released.
In wine terms, vintage does not have the nuance of "old and valuable" that is present in other terms such as vintage guitars and vintage jeans; it simply refers to the year the grapes were harvested . (Because older wines were often more valuable, the wine term "vintage" has come to be used as a general word to describe something old and good.)
When winemakers indicate a vintage, they must adhere to the "proportion of grapes used" determined by the country or region. In other words, as long as they follow this rule, they can mix wine made from grapes harvested in slightly different years, even if they are not 100% from the same harvest year.
Also, a year in which the grapes are of good quality is called a "great vintage" and the opposite is called an "off vintage".
Old vintage wines traded on the market tend to be more expensive if they are from great vintages, but less so if they are from off-vintage vintages.
In the Champagne region, in order to maintain a stable production volume, wine is often made by blending grapes from multiple harvest years, and 80% of wines do not state the harvest year. Such wines are sometimes labeled NV (non-vintage).
In French, vintage is called "millesime".
