Curd is obtained by coagulating milk in a sequential process called curdling. It can be a final dairy product or the first stage in cheesemaking.The coagulation can be caused by adding rennet, culture, or any edible acidic substance such as lemon juice or vinegar, and then allowing it to coagulate. The increased acidity causes the milk proteins (casein) to tangle into solid masses, or curds. Milk that has been left to sour (raw milk alone or pasteurized milk with added lactic acid bacteria) will also naturally produce curds, and sour milk cheeses are produced this way. Producing cheese curds is one of the first steps in cheesemaking; the curds are pressed and drained to varying amounts for different styles of cheese and different secondary agents (molds for blue cheeses, etc.) are introduced before the desired aging finishes the cheese.

The remaining liquid, which contains only whey proteins, is the whey. In cow's milk, 90 percent of the proteins are caseins. Curds can be used in baking or may be consumed as a snack.

Basically curd is a milk product that
is fermented, healthy and probiotic. Thus it is widely used in Indian cuisine to make a variety of recipes like dahi vada, papdi chaat, curd rice, kadhi pakora, chaas, lassi, raita, thepla etc.
It is also used as a marinade base to
make tikka recipes and also used in
the preparation of biryani. There are
also some sweets where yogurt is
one of the ingredient like shrikhand,
balushahi, mishti doi etc.