"Tteok" means rice cake, and "guk" indicates soup. The type of rice cake used for this soup is called garaetteok, which is unsweetened and looks like a white water hose. But nowadays you can get already sliced garaetteok (rice cake) from any Korean grocery shop; even in Korea, making the soup preparation much easy.
Often, Koreans add mandu (Korean dumplings) to tteokguk, in which case the soup is called tteok-manduguk. You can use any kind of mandu in the soup.
This starchy and soothing bowl of soup is not only a New Year's tradition but is classic comfort food any time of the year!