Qing Ming (清明) is a traditional Chinese festival on the 104th day after the winter solstice respectively the 15th day from the Spring Equinox. It usually occurs around April 5th of the Gregorian calendar.
After Qing Ming it usually gets hot and the rainy season (monsoon) starts. Therefore, tea harvested before Qing Ming is of superior quality. Tea harvested after this date but before the monsoon is often referred as "pre rain" tea.