It's April 20... or 4/20 and when the clock strikes 4:20 p.m., it's very likely that pot fans will light up in honor of Pot Day, according to CNN.
This date has become an opportunity for proponents of marijuana to campaign for its legalization across the country, and CNN noted that one of the biggest rallies is the smokeout on the University of Colorado campus at Boulder. Last year, an estimated 10,000 people came, from far and wide, to smoke the weed on the campus' quad.
The myths surrounding the significance of the number 420 include one version that says 420 is the police code for someone smoking pot and another that says it's the number of active chemicals found in marijuana, according to CNN.
Another theory says the origin of the number was a tribute to Bob Dylan's 1966 song "Rainy Day Women #12 & 35" which has the lyrics "Everybody must get stoned."
More on GlobalPost: 'Drug mules' caught transporting marijuana by donkey from Lesotho to South Africa
The Huffington Post put forward a more concrete theory. According to HuffPost, it all started with a lost patch of cannabis in a forest in Point Reyes, Calif., and a group of five San Rafael High School friends who coined the term.
The story goes: "One day in the fall of 1971 — harvest time — the Waldos got word of a Coast Guard service member who could no longer tend his plot of marijuana plants near the Point Reyes Peninsula Coast Guard station. A treasure map in hand, the Waldos decided to pluck some of the free bud."
The five friends, dubbed Waldos, agreed to meet at 4:20 p.m. to begin their search, and with each unsuccessful but high trip, the term quickly became a code word for smoking up. The working theory, said the HuffPost, is that the term spread through the Grateful Dead's rehearsals, concerts and parties.
The magazine High Times, dedicated to the legalization of marijuana, picked up the term and popularized it.
More on GlobalPost: Oaksterdam University, medical marijuana school, raided by feds
Reuters noted that marijuana is still illegal under federal law, but Colorado and Washington will vote on decriminalizing it in November. Having any amount of pot on you can result in criminal charges, with punishments ranging from a citation, probation or community service to fines and possible jail time.
The Atlantic provided some sobering statistics: "Calculations based on data provided by the Bureau of Prisons and the United States Sentencing Commission suggest that one of every six inmates in the federal prison system—roughly 15,000 people—has been incarcerated primarily for a marijuana offense."
Meanwhile, The Los Angeles Times noted that celebrations and protests planned for Denver, Colorado and Austin, Texas will begin at... yes, you guessed it: 4:20 p.m.
More on GlobalPost: Economic growth pulls Rwandans out of poverty