Definition - What does Grand Vin mean?
The term Grand Vin, which is often found on wine labels from the Bordeaux region, does not hold official meaning. However, it is often placed on a label to indicate that the wine is one of their best. Following the bottling of Cru wines, it falls behind the second bottling, or wine's from other vineyards not classified as Cru. Wineries use this term to market that it is their best wine.
WineFrog explains Grand Vin
In the New World, wine is not often labeled as "Grand Vin", however, depending on the estate and winery, they might have other titles they use which may be synonymous. While they hold no significance or follow any strict regulation, such terms are often used to indicate a special wine. It is a label used to say that the particular wine was made from specific vineyards or even smaller blocks within a vineyard. It is also used to indicate that the wine is the estate's "first wine" or first label under their estate. It can also be used to note that the Grand Vin is the first bottling of a vintage.