420 (cannabis culture)
From The Art and Popular Culture Encyclopedia
4:20 or 4/20 (pronounced four-twenty) is a term used in North America as a discreet way to refer to the consumption of cannabis and, by extension, a way to identify oneself with cannabis culture. Phrases such as "420 friendly" sometimes appear in roommate advertisements, indicating that the current occupants are tolerant of cannabis users.
Although many diverse theories exist to explain the origin of the term, it is widely accepted that in 1971, a group of teenagers at San Rafael High School in San Rafael, California, calling themselves "The Waldos", used to meet after school at 4:20 p.m. to smoke cannabis at the Louis Pasteur statue. The term became part of their group's salute, "420 Louis!", April 20 ("4/20" in U.S. dating shorthand) has evolved into a counterculture holiday, where people gather to celebrate and consume cannabis. In some cities, this celebration coincides with the celebrations of Earth Week.