So I'm going out on a limb and assuming that the question was legit. That guy Beppi isn't exactly correct BTW, esp regarding white wine.
Anyway, next time someone asks, tell them that there are different types of tannins. For example, gallotannins are hydrolyzable tannins and they're derivatives of 3,4,5-trihydroxyl benzoic acid, also known as gallic acid. That of course, can be esterified to a core polyol, and the galoyl groups can be further esterified or cross-linked to form more complex tannins.
There are other types of tannins of course. Ellagitannins for example, have higher oxidative activities at high pHs and that activity is thought to have an effect on caterpillars that you just don't get with the higher-molecular weight gallotannins.
That usually satisfies most people.