Late Harvest - is a specific term applied to a wine crafted from grapes which have been left to hang on the vine longer than normal. The term Late harvest is usually used to describe a sweet wine, sometimes called a 'dessert wine', with a common example being a Late Harvest Riesling. Late Harvest grapes typically look like hanging raisins, but they have naturally dehydrated - while still hanging onto the vine.
As a result of the dehydration of water within each berry (e.g. 30-40%), the grapes now measure higher levels of natural sugar compared to a normal plump, water filled grape. So when pressed the resulting juice is much sweeter and richer than other still wines. Riesling is a typical 'late harvest' wine grape used around the world.

 

Other grape varietals used include: Gewürztraminer, Furmint, Muscat, Pinot Gris, Sauvignon Blanc and Viognier to name just a few.
Many of the classic examples of late harvest sweet wines come from Europe. For example, the 'Vendange Tardive'(tranlsates to 'late harvest') are wines from the Alsace wine region in France, tend to be moderately sweet. Later harvested wines from Germany and Austria, of the 'Spätlese' and 'Auslese' designation for example, also tend to be moderately sweet.
In Germany, wines are classified according to the ripeness of the grape at the time of harvest. Within the Qualitatswein mit Pradikat classification, there are 4 levels of late harvest wines, roughly ranging from dry to very sweet: 'Spatlese'  - ('late harvest'), 'Auslese'('selected harvest'), 'Beerenauslese'('selected berries harvest') and 'Trockenbeerenauslese' - ('selected dried-berries harvest') with the last two levels being grape affected by botrytis.
The resulting high sugar content in the finished wine tends to be thick, sweet and very rich; some people find late harvest wines almost cloying because of the intense sweetness, while others simply can not get enough.
Be careful when trying to pair late harvest wines with sweet desserts - as the two don't always match each other's intensity - but when matched well with selected cheeses, lighter style desserts served cold and sweet freshly cut fruits they are a perfect end to a meal - plus many are at their best when enjoyed on their own - (60mls - served in a small glass).