Kashk is a range of dairy products used in cuisines of Iranian, Afghan, Turkish, Mongolian, Central Asian, Transcaucasian and the Levantine people. Kashk is made from drained yogurt (in particular, drained qatiq) or drained sour milk by forming it and letting it dry.
The Persian "kashk" is a preserved food made from wheat or barley mixed with sour milk or yoghurt; in Iran, however, the same word also means dried buttermilk. Kashk comes in liquid or dried form (you reconstitute it with water), and is traditionally made with the milk left over from cheese-making..
In Turkey, kashk is a dried yoghurt product also known as keş peyniri, kurut, taş yoğurt, kuru yoğurt, or katık keşi.
In modern Iran, kashk is a thick whitish liquid similar to whey or sour cream, used in traditional Persian cuisine like ash reshteh, kashk e badamjan, kale joush. It is available as a liquid or in a dried form, which needs to be soaked and softened before it can be used in cooking. Kashk was traditionally produced from the leftovers of cheese-making .