Smetana is a Slavic loanword in English for a dairy product that is produced by souring heavy cream. Smetana is from Central and Eastern Europe, a soured cream product like crème fraîche (28%), but much heavier and thicker with usually 36% to 42 % milkfat or even higher, more sour in taste than crème fraîche. It will not curdle when cooked or added to hot dishes. Its cooking properties are different from crème fraîche and the lighter sour creams sold in the U.S., which contain 12 to 16 percent butterfat.
Smetana is called Smetana in Russian and Ukrainian (written сметана in the Cyrillic alphabet) and in Finnish , smiatana in Belarusian, Schmetten or Schmand in German, śmietana in Polish, Shmetana in Yiddish, kvasena smetana in Bulgarian, Smotana in Slovak, zakysaná smetana in Czech, and smetana or kisla smetana in Slovenian.
In Hungarian it is called Tejföl or Tejfel and in Romanian Smântână, in Estonian Hapukoor, in Lithuanian Grietinė, in Latvian Skābs krējums, in Serbian and Macedonian Pavlaka or Mileram, in Bosnian Pavlaka, in Albanian Shtalpë and in Croatian Kiselo vrhnje.
Smetana is widely used in many Eastern European cuisines: in appetizers, main courses, soups and desserts. For example, it may be blended into local soups, vegetable and meat dishes, or cole slaw; served with pelmeni, dumplings, or pierogi; or used as a filling in savoury pancakes. Smetana can be blended to a Liptauer-like cheese spread with local cottage cheeses, onions, paprika and other spices, eaten with bread. It is often used in cooking, as it is high enough in fat not to curdle at higher temperatures. It is used in the preparation of meat or vegetable stews and casseroles, or other dishes that require a long cooking time in the oven. Smetana doesn't melt in the oven and it doesn't soak the whole dish like crème fraîche. Hungarian cooks use it as an ingredient in sauces like paprikas and in recipes such as ham-filled crepes (palacsinta). The current trend to reduce fat content of the milk products has caused the taste and consistency of many milk products to deteriorate. To imitate Hungarian style cooking and the use of Smetana (called Tejföl in Hungarian), Hungarian cookbooks recommend using Western sour cream mixed with heavy whipping cream (38–40% milkfat). Homogenization breaks the fat into smaller sizes. Smetana is not homogenized.
Smetana is also widely used in Finnish cooking,  smetana being more commonly used in Karelia and Ingria. In Ukrainian and Russian cuisine, sour cream is often added to borscht and other soups, and is used as a condiment for dumplings like vareniki and pelmeni.
Almost all Croatian dairies produce smetana, but connoisseurs hold that only that purchased from a milkmaid selling her own products, often at a farmers' market, is the real item. Eurosceptics feel that local products would disappear under the European standardization (BBC News article).
When comparing brands or suppliers of smetana, the Polish and Russian practice is to compare the fat content of the varieties. Fat content can range from 10% (runny) to 70% (thick). The most common supermarket smetanas are 10 to 40% fat (milk fat only for an authentic product). Addition of thickeners such as gelatine is not forbidden by relevant regulations, but is regarded as cheating and the product is considered substandard and unsuitable for culinary use, since some recipes are easily spoiled by the presence of a thickener.