Cultured buttermilk is a yogurt based buttermilk (made by active cultures) inoculated with live bacteria to simulate the natural process by withch traditional buttermilk is made. The standard buttermilk you will often find is traditionally made via a bi product of butter churning. Milk is left to separate out and naturally ferments. This helps the churning but produces a natural liquor aka buttermilk!

When it comes to baking, the natural buttermilk and "cultured" buttermilk don't differ in that they don't really have much effect on the final structure of the baked good. Cultured buttermilk, depending on the source, can have a slightly lower fat content but it is often negligible. A lot of chefs and home cooks argue over taste differences but that is the biggest difference I have found. It's just a matter if experimenting to see such one you like best :)

Either product should work just fine in almost any recipe

Hope this helps!

Yes! I use the two kinds interchangeably in baked goods. Wonderful stuff! ;o)