Complex sentence: A vintage wine is one whose grapes were all grown in a single specified year, although common incorrect usage applies the term to any wine that is perceived to be particularly old or of a particularly high quality.
Split into simpler sentences: A vintage wine is one made from grapes that were all grown in a single specified year. 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.