Mid-Autumn Festival or also commonly known as Moon Cake Festival is celebrated on the 15th day of the eight month on the Chinese Lunar Calendar. Why it is called Moon Cake Festival, there seems to be many myths/stories behind.
One such story was in the 14th century when China was in revolt against the Mongols. The Chinese troops secretly hid messages in the moon cakes advising the coordination on an uprising. These moon cakes were distributed to the people during the mid-autumn festival. They overthrew the Mongols and the moon cakes became even more famous.