420 is slang in cannabis culture for the consumption of cannabis, especially smoking cannabis around the time 4:20 p.m. and smoking cannabis in celebration on the date April 20.
In 1971, five high school students – Steve Capper, Dave Reddix, Jeffrey Noel, Larry Schwartz, and Mark Gravich in San Rafael, California, calling themselves the Waldos because "their chosen hang-out spot was a wall outside the school", used the term in connection with a 1971 plan to search for an abandoned cannabis crop that they had learned about, based on a treasure map made by the grower. 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 plan with the phrase "4:20 Louis". After several failed attempts to find the crop, the group eventually shortened their phrase to simply "4:20", which ultimately evolved into a code-word that the teens used to mean consuming cannabis.
Statue of Louis Pasteur created by Benny Bufano at San Rafael High School.
Thousands illegally consume cannabis in Golden Gate Park to celebrate 420 and end prohibition, April 20, 2013.