What is the difference between a Nebbiolo and a Barolo and Barbaresco?

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Dear Dr. Vinny,

What is the difference between a Nebbiolo and a Barolo and Barbaresco? I
know the two "B's" are made from the Nebbiolo grape, but what characterizes
a Nebbiolo wine?

-Kathryn, Los Angeles

Dear Kathryn,

You're correct that Nebbiolo is both the name of a grape and of a wine made
from that grape. Though small amounts of Nebbiolo are grown all over the
world, it's mostly found in northern Italy, in the Piedmont region. Within
Piedmont are two wine-producing zones called Barolo and Barbaresco, whose
namesake wines are both made from the Nebbiolo grape. A wine may be labeled
as a Nebbiolo if it's made in a region outside Barolo and Barbaresco that
permits varietal labeling.

What characterizes Nebbiolo and the wines of Barolo and Barbaresco? I find
the wines very distinctive, with aromatic tar, rose, licorice and truffle
notes. The wines can be a highly tannic and have a reputation for aging
well. In general terms, Barolo is the more massive, tannic and rich of the
two, while Barbaresco is considered more elegant and approachable.

-Dr. Vinny