Vendange Tardive ('VT') simply means 'late harvest' in French. The phrase refers to a style of dessert wine where the grapes are allowed to hang on the vine late into the growing season - until they start to dehydrate, shrivel on the bunch.
This process, called passerillage, concentrates the sugars in the grape juice and changes the flavours within the berry. The name is sometimes written as the plural form, vendanges tardives, referring to the fact that several runs/ passes through the vineyard, harvesting select bunches and even single berries, is often necessary to produce such wines.
Alsace wines were the first to be described as vendange tardive but the term is now used in other wine regions of France.
Since 1984, the term has been legally defined in Alsace and may only be applied to wines that exceed a minimum must weight and pass blind tasting by the INAO.
Selection de Grains Nobles ('SGN') is an even sweeter category, for grapes affected by noble rot (botrytis cinerea). Vendange Tardive is also an official wine designation for the sweet wines which are produced in Luxembourg.
Since German is a common language in the Alsace region along with French (as Alsace was controlled by Germany four times in its history, being again part of France since the end of world war one), the designation vendange tardive is often translated literally as Spatlese by the Alsatians. However, the must weight requirement for a 'VT' is higher than for the Pradikat Spatlese in Germany or Austria. In wine classification terms, a Vendange Tardive wine from Alsace is more close to a German or Austrian Auslese.
Gewürztraminer is the most common grape variety used for vendange tardive wines, as it readily achieves high sugar levels; these are harder to attain with Riesling and Pinot Gris, but with greater acidity to balance the sweetness, such wines can be very long-lived. Muscat vendange tardive wines are also sometimes seen when the vintage and vineyard is suitable.