Short answers, pulled from the story.
Smetana is a type of sour cream traditionally prevalent in Central, Eastern, and Southeastern Europe and Central Asia. It is produced by souring heavy cream and typically contains between 9% and 42% milkfat depending on the country.
American sour cream contains around 18% butterfat and can curdle at higher cooking temperatures. Smetana has a higher fat content and is not homogenized, allowing it to hold together through long, slow cooking in stews, sauces, and oven dishes without separating.
Smetana is used in beef Stroganoff, borscht, pierogi, pelmeni, varenyky, paprikas sauces, hortobágyi palacsinta, bryndzové halušky, marinated beef svíčková, and Liptauer-style cheese spreads. It appears in appetizers, main courses, soups, and desserts across Central and Eastern European cuisines.
Smetana comes from the common Slavic root "sъmętana", derived from the verb "sъmětati", meaning to remove or to dump. The name reflects the process of skimming cream from the top of milk. Variations of the word appear in Russian, Ukrainian, Belarusian, Polish, Slovak, Czech, Slovenian, Serbian, Bulgarian, Romanian, and Finnish.
Smetana fat content ranges from 10% at the runny end to 70% at the thickest. Supermarkets typically stock the 10%-40% range. In Central European countries, smetana must contain at least 10% fat, and versions with at least 30% fat are designated as whipping cream.
Smântână is a Romanian dairy product produced by separating milkfat from milk through decantation rather than by souring the cream. Its taste is tangy and sweet, and soured smântână is considered spoiled rather than desirable. It is used in ciorbă, alongside mămăligă, and with sarmale.