Qingming Festival (清明节), Pure Brightness Festival in English, is a traditional Chinese festival on the 104th day after the winter solstice, usually occurring around April 5 of the Gregorian calendar. The name of this festival denotes a time for people to go outside and enjoy the greenery of springtime and tend to the graves of departed ones.
This set of 3 stamps featured on this envelope illustrates this traditional festival. The last stamp (50分) portrays construction on Hainan Island. Thank you very much Hai Huang! -_-