420, 4:20 or 4/20 (pronounced four-twenty) refers to consumption of cannabis and, by extension, a way to identify oneself with cannabis subculture. 4/20 is sometimes referred to as "Weed Day" or "Pot Day"

The term was coined from a group of teenagers at San Rafael High School in San Rafael, California, United States in 1971. The teens would meet after school at 4:20 p.m. to smoke marijuana outside the school.

According to an April 2009 article on the The Huffington Post, the group called itself the Waldos because its members hung out by a wall after school. Writer Ryan Grim, citing interviews with anonymous Waldos, claims that the group met by the statue at 4:20 p.m. to begin a search for a crop of abandoned cannabis growing near Point Reyes that they had heard about. They never found the stash, Grim writes, but smoked plenty of marijuana while looking for it.