holidays
Cold Food Festival, held on April 4 if it is a leap year (China); and its related observances:
Related Wikipedia articles
Cold Food Festival
Traditional East Asian festival
The Cold Food or Hanshi Festival (寒食节) is a traditional Chinese holiday which developed from the local commemoration of the death of the Jin nobleman Jie Zitui in the 7th century BC under the Zhou dynasty, into an occasion across East Asia for the commemoration and veneration of…Source: Wikipedia (CC BY-SA)
Leap year
Calendar year with a day (or month) added
A leap year is a calendar year that contains an additional day compared to a common year. The 366th day is added to keep the calendar year synchronised with the astronomical year or seasonal year. Since astronomical events and seasons do not repeat in a whole number of days,…Source: Wikipedia (CC BY-SA)