Yes, buttermilk is a milk product, but no, it does not contain actual butter per say. However, in the old days it was made from the sour, residual liquid that remained after the butter was churned. You could often see little flecks of butter in the milk that were misplaced during the skimming process.
Many people are surprised to learn that buttermilk is no higher in fat than regular whole milk, it does however have more sodium, about 240 mg per cup. It is thicker with a creamier texture than regular milk, but not quite as thick as cream. There are a few low fat low sodium buttermilk varieties available including one from Friendship Dairies, but we haven't been able to try them yet.
Buttermilk is often used in baking and it's classic taste adds a delightful, almost sour flavor to biscuits, pancakes, waffles, cookies, pies, donuts, bread and more. I also like the flavor and texture it adds to fried chicken, batters, marinades, sauces and salad dressings. It's a wonderful cooking secret.
For the record, there are different kinds of buttermilk, which vary by production and flavor - Traditional, also known as "natural" or "ordinary" buttermilk, is made the old fashioned way from the residual liquid produced during the butter churning process; Cultured, also known as "artificial", is artificially made utilizing whole milk and lactic acid bacteria; Bulgarian, a cultured buttermilk also, but one which uses a different strain of bacteria for a slightly tarter taste; and, Acidified buttermilk which is made by adding a food-grade acid product.