Sour cream is a food made from cream that has been fermented. It is thicker than cream, and has a sour taste from lactic acid. Sometimes when bought from a store it has gelatin, rennet, or other things added to make it thicker. Like many other dairy products, it must be kept refrigerated.
Sour cream is used in many European and American foods. It is used as a sauce for baked potatoes, and as a dressing for salads. Sometimes it is in baked goods like cheesecake and doughnuts. It can be mixed with sugar to make an icing for cakes.