Japan has four distinct seasons: spring, summer, autumn, and winter. The term setsubun originally referred to the days marking the change from one season to the next, so that there were four of them, but today only the day before risshun (the beginning of spring in the traditional Japanese calendar) is called by that name. Setsubun comes on either February 3 or 4, depending on the year.
... I am so sorry, but this post has been moved to my new website, The Pagan Calendar, and can be found in its entirety here: Setsubun