That's Noble Rot to you... 

Botrytis Cinerea is a fungus that forms on ripe grapes, piercing the skin with tiny holes and allowing for water to evaporate out of the grape, intensifying the sugars, acids, and flavours that remain. It creates dried apricot, honey, and ginger flavours, among other things. 

It needs specific conditions to be beneficial - specifically humid, misty mornings for the fungus to develop coupled with sunny afternoons for the water in the grapes to evaporate.  Some of the great wines of the world are made using botrytised grapes; the sweet wines of Tokaji, Sauternes (in Bordeaux), and the Mosel most notably. All of which are near rivers, importantly, which aides in creating the right weather conditions or terroir (I think - still don't fully know what that word means). 

Yields are tiny, and the resulting wine is very expensive, but if you have been known to wave off the ice-cream menu and opt instead for a glass of sticky at the end of a meal, then you should add 'splurge on a bottle of Château d'Yquem' to your bucket list.