It is called 'Naengmyeon (냉면; 冷麵, in South Korea) or raengmyŏn (랭면, in North Korea)'.
The noodle is made from the flour and starch of various ingredients. This dish is served cold and considered as a summer dish. However, it was not until the late 19th century that naengmyeon was considered a summer food.
There are two main types of naengmyeon: mul naengmyeon (물 냉면) and bibim naengmyeon (비빔 냉면).
Mul naengmyeon is served as a cold soup with the noodles in beef, chicken or dongchimi broth.
Bibim naengmyeon is served with gochujang (고추장: spicy red chili paste) sauce on top of noodle.
In restaurants, the dish is served with garnishes such as slices of radish, slices of boiled meat, cucumbers, pears and hard-boiled eggs. You can add vinegar, mustard sauce or sugar before mixing to eat.
There are some famous restaurants specialized only in naengmyeon. I myself enjoy naengmyeon at least two or three times in summer time. You'd never imagine the nice tangy taste of the dish! It's so cool in hot summer days~
(Some of the photo shots are taken by me, and some are from public sites including Pixabay)