What does the term "reserve" mean on a wine label?
It usually means an inflated price. Beyond that, it's hard to be definitive.
There's no international standard for the designation. Historically it referred to a wine deemed of higher quality by its producer. When a parcel of land yielded exceptionally concentrated grapes because of location and weather, the winemaker would hold the wine aside – "reserve" it – and lavish it with extended barrel time. These wines tended not only to taste richer but to cellar better as well.
That's the case with some reserve wines today, but certainly not all. Some regions, notably in Europe, regulate the term. A Chianti Riserva, for example, must spend a prolonged period maturing before release to meet the requirement, and usually producers only set aside their best juice for such treatment. In many other regions, they're free to use the term merely as a marketing tool. Kendall-Jackson in California, for example, calls its flagship chardonnay Vintner's Reserve – but there's no non-reserve counterpart.
Do reserve wines – whether genuinely held back for quality's sake or not – always taste better? No. I often prefer regular Chiantis to the same producer's riserva bottling. It may lack the riserva's concentration and cellar-worthiness, but often there's a more cheerfully bright profile to regular Chianti that is, I think, masked by the vanilla overtones of long-term barrel aging. And it invariably costs less. When it comes to wine, a higher price is no guarantee of superior pleasure.