One of the Dimensions Of Wine > Core Dimensions.
Bitterness, usually referred to as Tannin.
Drying, not Dry.
High amounts of Tannin will make your mouth feel dry, but that doesn’t mean it makes a wine “dry”. A Dry wine specifically means one that’s low-Sugar.
Tannin is a bit like the “feels like” temperature caused by windchill. It feels colder than it actually is.
Color
Tannin is usually present in the skins of fruit (like grape skin), and so is present along with more color. A red wine has grape skins, and so has tannin – white wines have the skins removed, and have little to no tannin.
Tannin = Color = Bitterness
Tannin is the thing tanning your wine. More color means more tannin. Red wines are more bitter than white wines.
Tannins in wine can also come from wood storing (oak aging).
Aging
A wine with very strong tannins is often better when aged. Years of storing in a bottle will soften the tannins. This is why a finely aged wine usually means a red wine, because aging specifically affects the red parts of it.
Health
Tannin is present in skins as an insect & pest repellant.
In humans, they are antioxidant and antibacterial. This is why you may have seen a doctors recommendation to drink 1 glass of Red wine a day.