Quark is a type of fresh cheese

Cheese

Cheese is a generic term for a diverse group of milk-based food products. Cheese is produced throughout the world in wide-ranging flavors, textures, and forms....

, also known as tvorog (from the Russian творог), topfen (from the Austrian

Austrian German

Austrian German , or Austrian Standard German, is the national standard variety of the German language spoken in Austria and in the autonomous Province of South Tyrol...

 name), biezpiens (from Latvian), and varškė (from Lithuanian). It is made by warming soured milk until the desired degree of denaturation of milk proteins is met, and then strained. Dictionaries usually translate it as curd

Curd

Curds are a dairy product obtained by curdling milk with rennet or an edible acidic substance such as lemon juice or vinegar, and then draining off the liquid portion. The increased acidity causes the milk proteins to tangle into solid masses, or curds. The remaining liquid, which contains only...

 cheese or cottage cheese

Cottage cheese

Cottage cheese is a cheese curd product with a mild flavor. It is drained, but not pressed, so some whey remains and the individual curds remain loose. The curd is usually washed to remove acidity, giving sweet curd cheese. It is not aged or colored. Different styles of cottage cheese are made from...

, although most commercial varieties of cottage cheese are made with rennet

Rennet

Rennet is a complex of enzymes produced in any mammalian stomach to digest the mother's milk, and is often used in the production of cheese. Rennet contains many enzymes, including a proteolytic enzyme that coagulates the milk, causing it to separate into solids and liquid...

, whereas traditional quark is not.