4:20 or 4/20 is a term that refers to the consumption of cannabis in the American cannabis culture. In North America, April 20 (4/20 in US date format) is a holiday of the counterculture, which this illicit drug is publicly used and its existence celebrated.
The concept may find its origin in 1971 in California, where a group of teenagers at San Rafael High School, ‘Waldos’ named after school at 16:20 (4:20 pm) would be gathered to marijuana smoking. According to an article in April 2009 by The Huffington Post called the group the Waldos because its members at a wall (English: wall) would hang around the school. The meeting was started as gathering of people was looking for some unguarded cannabis plants were located at Point Reyes. Although not found the plants were much smoked cannabis while searching and increased the time to become a regular meeting to smoke cannabis.
Over the years, the concept became a phenomenon and was an April 20 date is consumed cannabis in many places and the existence of the plant is celebrated. The day is also used to demonstrate against the marijuana prohibition.