Zongzi is a traditional food for celebrating Dragon Boat Festival which is on the 5th of May according to the Chinese lunar calendar.
The Dragon Boat Festival is traditional customs to attempts to rescue the patriotic poet Chu Yuan. Chu Yuan drowned on the fifth day of the fifth lunar month in 277 B.C.
Chinese citizens throw bamboo leaves filled with cooked rice into the water.
Therefore the fish could eat the rice rather than the hero poet.
This later on turned into the custom of eating rice dumplings.