Qingming Festival, also known as Tomb Sweeping Day or Pure Brightness Festival, is a traditional Chinese festival observed on the 15th day after the spring equinox (usually falling on April 4th or 5th). 

The festival is a time for Chinese people to pay respect to their ancestors by visiting and cleaning their graves. It is believed that during the festival, the spirits of the ancestors return to the world of the living, and people must show their respect and gratitude by offering food, incense, and other offerings at the gravesite. 

Apart from tomb sweeping, people also engage in other activities during the festival, such as flying kites, wearing willow branches, and enjoying traditional food such as qingtuan (a glutinous rice cake) and green tea. 

Qingming Festival is not only observed in China but also in other countries with a significant Chinese population, such as Taiwan, Hong Kong, and Singapore.