In Indian chaas buttermilk terms are used interchangeably. In english "Chaas" is called as "Buttermilk". Technically chaas is the leftover liquid after butter is churned out of cream. In old days, this liquid was served by adding salt & cumin powder with the meal and known as chaas. It was a great probiotic drink for digestive system. Now we do not consume this leftover liquid, rather make chaas using homemade curd, water, salt & cumin powder.