Definition - What does Bottle Aging mean?
In the context of winemaking, bottle aging simply means that a wine is aged in its bottle and is not aged in bulk in a cask, oak barrel, barrique or other large vessel. Historically, wine was aged in wooden barrels, but due to innovations in glass molding technology during the 17th and 18th century, glass became an obvious vessel to age wine in. Glass bottles prevent oxidation and leakage and as the glass does not interact with the wine, it allows for a more consistent aging of wine.
WineFrog explains Bottle Aging
Since the early days of wine making, it has been recognized that aging can improve and develop complex flavors in wine. As wine ages, complex chemical reactions continue to occur that affect change in taste and mouthfeel of wines. Bottle aging has historically had advantages over bulk aging, as large containers were more susceptible to oxidation and leakage and bottle aging produced more consistent wines from the vintage. When wine is bottle aged it has to be stored away from light in a temperature and humidity controlled environment.