The number 420 (pronounced four-twenty) is the not-so-secret code for cannabis consumption and culture. The commonly held belief is that 420 originally referred to a smoking time, 4:20pm in the afternoon, but today the most popular reference is April 20 (4/20), which is unofficially world cannabis day. Covering both bases, cannabis aficionados typically celebrate the 4/20 holiday by lighting up at 4:20pm, sometimes in large public gatherings.
Over the decades, countless theories postulated different 420 origins, but most people now believe it originated in 1971 with a group of teen hippies in the Bay Area. If true, this means 420 originally referred to a search for cannabis, not actually smoking the plant, though the meaning quickly evolved among the teens and their social connections.