Mandu are Chinese dumplings made from flour, meat, and vegetables chopped in very small pieces. Slightly chopped meat, and vegetables are mixed together, called so (소) in Korean. Then a handful of so is wrapped by a piece of slice dough which prevents so from spreading out. These small balls are cooked in various ways. They can be grilled, fried, boiled, or even steamed, so that each of them has different name. These Mandu are usually served with dipping soy sauce mixed with vinegar.
Originally, mandu are from China. They were introduced in Korea in the middle of Chosun dynasty, and have become to have their own recipe in Korea. Chinese call tteok which does not contain so mandu, and call flour balls stuffed with so gyoza. While mandu (gyoza in Chinese) are served in usual days in China, they are traditionally made only in the early winter or in a big party in Korea (Nowadays, they are easily seen in the every season, every day in Korea).
Meat for so can be various. Pork is the most common meat for mandu, and beef, chicken, or pheasant also can be ingredients of mandu. Vegetables contained in so are usually carrots, cucumbers, onions, and mug-bean sprouts. Sometimes kimchi is used for so. Other additional ingredients are tofu, or chopped noodle made from sweat potatoes.