As legend goes, the history of 420 originates in 1971 in California. Five high school students in San Rafael used the term “4:20” in connection with their plan to search for an abandoned cannabis crop (based on a treasure map made by the grower).
The group called themselves the “Waldos,” since their hangout was a wall beside the school. 4:20 was their meeting time to search for the crop. Though ultimately unsuccessful, the time designation stuck and has been used ever since as a universal time to partake in cannabis 🙂 Source Wikipedia
Today it is a holiday celebrated socially and politically – a day to enjoy cannabis and also reduce the stigmas surrounding it’s use.