Originally buttermilk was made in the process of churning butter from cream. The leftover liquid is buttermilk. This was called traditional buttermilk. These days commercially available buttermilk which is also known as cultured buttermilk is made by fermenting dairy milk with bacterial culture. Back in those days this cultured buttermilk was called artificial buttermilk to denote that traditional buttermilk was natural buttermilk. These days even powdered buttermilk is available which can be mixed with water to get the liquid form.
Yogurt is made by fermenting cow’s milk using yogurt cultures. The fermentation process converts the lactose into lactic acid and that gives it the tangy taste.
Both buttermilk and yogurt come in low fat and non-fat varieties.