The curd is the dairy product obtained by coagulating milk with organic compound or an edible acidic substance like vinegar or lemon juice and then draining off the whey or the liquid portion. Milk, which has become sour like raw milk alone or pasteurized milk with the addition of lactic acid bacteria, also produces curd naturally. The increased acidity causes the casein or milk proteins to tangle into solid masses or curds. The liquid part only contains whey protein. In cow milk 80% of the proteins are caseins.

In India, curd is a vegetarian food that is prepared by using yeast to ferment the milk. In Indian subcontinent, buffalo milk is used to prepare curd due to its higher fat content to make a thicker curd. The quality of curd depends on the starter used to curdle. The time for curdle also varies from season to season.

According to Ayurveda curd has many beneficial value, especially in digestion. Curd is also used as a sacred symbol in all the Hindu rituals.