Hello, Emme! Here is a description of buttermilk from Wikipedia: Basically, it’s milk that has been soured with bacteria. I was looking for other names for it and I found kefir, piima, and talouspiima. I’m not exactly sure those are the same thing. They may actually be more like yogurt. While I was searching, I found this link and found it pretty amusing!!! Ask Mr. Breakfast, “What is Buttermilk?” http://www.mrbreakfast.com/ask.asp?askid=18 Also, whey can be substituted for buttermilk in many recipes. When I make yogurt I always drain off some of the whey to make pancakes the next day... delicious!!