420, 4:20, or 4/20 (pronounced four-twenty) is a code-term that refers to the consumption of cannabis and by extension, as a way to identify oneself with cannabis subculture or simply cannabis itself. Observances based on the number 420 include smoking cannabis around the time 4:20 p.m. (with some sources also indicating 4:20 a.m.) on any given day, as well as smoking and celebrating cannabis on the date April 20 (4/20 in U.S. form).
A group of teenagers in San Rafael, California, calling themselves the Waldos began using the term in connection with a plan to search for an abandoned cannabis crop that they had learned about in autumn 1971. Although their typical "hang-out spot was a wall outside the school," the Waldos designated the Louis Pasteur statue on the grounds of San Rafael High School as their meeting place, and 4:20 p.m. as their meeting time. The Waldos referred to this initial plan with the phrase "4:20 Louis", but after multiple attempts to find the crop failed, the phrase evolved in form and use—shortened simply to "4:20", the teens increasingly relied on the codeword to refer to pot-smoking in general.High Times, particularly the editor Steven Hager, was responsible for bringing the Waldos' story to a national audience. Hager called for 4:20 p.m. to be the socially accepted time of day to consume cannabis and attributed the early spread of the phrase to Grateful Dead followers, who were also linked to the city of San Rafael.
April 20 observances
420 event in Golden Gate Park, San Francisco, April 20, 2013
^ abMcKinley, Jesse (April 19, 2009). "Marijuana Advocates Point to Signs of Change". The New York Times. Archived from the original on 20 January 2011. Retrieved January 23, 2011. "Mr. Hager said the significance of April 20 dates to a ritual begun in the early 1970s in which a group of Northern California teenagers smoked cannabis every day at 4:20 p.m. Word of the ritual spread and expanded to a yearly event in various places. Soon, cannabis aficionados were using "420" as a code for smoking and using it as a sign-off on flyers for concerts where the drug would be plentiful. In recent years, the April 20 events have become so widespread that several colleges have discouraged students from participating. At the University of Colorado, Boulder, where thousands of students regularly use the day to light up in the quad, administrators sent an e-mail message this month pleading with students not to "participate in unlawful activity that debases the reputation of your university and degree.""
(Federal) = Federal holidays, (State) = State holidays, (Religious) = Religious holidays, (Week) = Weeklong holidays, (Month) = Monthlong holidays, (36) = Title 36 Observances and Ceremonies Bolded text indicates major holidays that are commonly celebrated by Americans, which often represents the major celebration of the month.