From Wikipedia: Mochi is a Japanese rice cake made of glutinous rice pounded into paste and molded into shape. In Japan it is traditionally made in a ceremony called mochitsuki. While also eaten year-round, mochi is a traditional food for the Japanese New Year and is commonly sold and eaten during that time. Mochi is also a prominent snack in Hawaii and Taiwan.
edit: also tagged this as Korean, where similar rice confections known as "Tteok" are available--see wikipedia: en.wikipedia.org/wiki/Tteok