Second wine or a second label is a term widely common with Bordeaux that refers to the release of an estate's wine under a second label, and not its prestigious first label. The second wine is selected from a blend (cuvee) not chosen for use in the final Grand Vin bottled with the first label. While there are many reasons why a finished blend is not released as the first label, the relative success or failure of a vintage or an inability to produce the optimum style of wine the Chateaux are known for are principal considerations that determine what wines make it to the first label, and which get cut to a second or private label.
Because of average or poor vintages an estate may decide to release only a second label wine rather than risk a first label that would not be consistent with past vintages or its very individual style. Many of the second label wines offer good value because the wines are usually great, just not great enough to demand a premium price, achieve good reviews or most importantly satisfy loyal fans. The practice is old, but became prominent in the '80s when consumers discovered second label wines a more affordable way to drink a French first growth or classified Bordeaux without paying a premium for the estate's first label.
The model has taken hold in the US and in most new world wine producing countries. It's kind of new and it may seem to be a bit of a mystery or a little secretive; it isn't as easy as Bordeaux to figure-out the who, what and where. There is lots of wine out there so alternate labels make sense to a winery that wants to sell all its wine. Some well known wineries are releasing very good wine as second labels or private labels (private labels are exclusive to national chains, better wine shops and restaurants). California wineries, even with their great Napa Cabs, face the same realities of excess wine, the effects of vintage, quality and style, the model works well for them. Whether there is too much wine produced, the economy, the vintage, the style, whatever the reason... there is good wine out there at reduced prices; everyone wins. So go ahead, be brave and travel the mean streets of wine, but remember the facts:
1) there is a lot of wine from around the world putting extreme pressure on suppliers and retailers to lower prices and encourage more consumption
2) not only are there second labels, but new brand extensions and new labels, as well as a proliferation of private labels
3) beware of cleverly marketed 'so-called' second label or wine club offers that purport to be 'de-classified' from higher priced American and European appellations or wine from very fine wineries that can only be found through non-winery or wine club internet sites.