Definition - What does Carboy mean?
A carboy is a holding vessel with a volume of 6.5 gallons that can be made of plastic or glass. Homebrewers or winemakers use it to make wine, mead, cider, beer or other alcoholic beverages. It is topped with a rubber stopper or a fermentation lock to prevent oxygen and bacteria from getting in during fermentation.
WineFrog explains Carboy
A carboy is sometimes referred to as a Demijohn. A DemiJohn was originally a glass vessel that had a large body and small neck, which was enclosed in a wicker basket. The basket made it easier to handle but also protected it during transportation.
They range in size from just over 1 gallon (approximately 4 liters) and go up to over 6.5 gallons (25 liters).
During homebrewing or winemaking, a primary carboy will be used for fermentation. When the fermentation is done, it is then transferred to another carboy. This is called racking.
For home winemakers, carboys are essential tools.