Botrytis cinerea, a.k.a. Noble Rot (noun): a kind of mold that grows on grapes late in the growing season.
But don't let the idea of moldy grapes fool you! This noblest of rots is a crucial component to many fine wines.
When noble rot sets in, the grapes shrivel up like raisins, concentrating the sugar inside. Much of this sugar remains after the grapes are fermented, eventually producing an intensely sweet white wine.