April 20 is the day when people from across America gather at pre-decided venues to celebrate the weed or marijuana culture, irrespective of whether it is legal in their states or not.

Rallies are organized in different states around the country, especially in California and Colorado where marijuana is legal. Pot smokers participate in record numbers in these rallies, either to just enjoy the day with friends or to show their support for the legalization of the drug.

There are quite a few mysteries surrounding the particular date Weed Day is observed on:

1. The Number 420: Yes, it’s the date when the love of cannabis is celebrated across the nation, but why this particular day? There are quite a few explanations/theories surrounding the number 420.

According to an urban myth, the penal code in California was 420 and was often referred to by police officers at the time for marijuana use. However the myth was debunked long ago.

Another unproven theory suggested a group of five students from the San Rafael High School went looking for a plot near the Point Reyes Peninsula Coast Guard Station, where they were growing pot. They met exactly at 4:20 p.m. to search for the plot, which was never located. However, 420 soon became a code among youngsters for smoking weed.

420 April 20 is the day when people from across America gather at pre-decided venues to celebrate the weed or marijuana culture, irrespective of whether the drug is legal in their states or not. In this photo, a person smokes marijuana during a 420 Day celebration on "Hippie Hill" in Golden Gate Park in San Francisco, April 20, 2010. Photo: Getty Images/ Justin Sullivan

2. The Band That Made The Term Popular: “Grateful Dead” and their fans (commonly known as the "Deadheads") are commonly credited for popularizing "420," Mic reported. 

3. Daniel 4:20 Points To A Tree: Although it might sound farfetched and probably offensive to many, this coincidence is too good to ignore. In the Bible, Daniel 4:20 reads: “The tree you saw, which grew large and strong, with its top touching the sky, visible to the whole earth, with beautiful leaves and abundant fruit, providing food for all, giving shelter to the wild animals, and having nesting places in its branches for the birds— Your Majesty, you are that tree! You have become great and strong; your greatness has grown until it reaches the sky, and your dominion extends to distant parts of the earth.”

4. Use Of 420 In California Weed Laws: California, the first state in the United States to legalize marijuana — for both medical and the recreational use — calls its senate bill number for the state's "Medical Marijuana Program Act" – “SB 420.”

5. 420 Chemicals: It was incorrectly believed there were 420 chemicals in marijuana. But according to the Dutch Association for Legal Cannabis and Its Constituents as Medicine, it has been proven there are in fact more than 500 active ingredients in marijuana. Only about 70 of them are cannabinoids unique to the plant.

Marijuana A marijuana user rolls a joint during a 420 Day celebration on "Hippie Hill" in Golden Gate Park in San Francisco, April 20, 2010. Photo: Getty Images/ Justin Sullivan

6. 420 In Short Story: In the short story "In the Walls of Eryx" by H.P. Lovecraft and Kenneth Sterling, the narrator talks about “curious mirage-plants.” The plants sound similar to marijuana plants and coincidentally made the narrator high when his watch struck 4:20, Vox reported. 

The significance of the day has evolved over the years. While in the early 1970s, 4/20 used to be observed by a fairly small number of people who embraced marijuana as a symbol to protest against some of the bigger issues facing the country, like overseas wars and how corporations were driving America. 

Today, however, the number had grown remarkably, and while there are still people who simply visit the rallies on the day to have a good time, most of the population consists of activists demanding the legalization of weed in their respective states.