At 4:20pm, thousands around the world will participate in a synchronized smoke-off.

A cloud of smoke is wafting across cities worldwide today with the celebration of 4/20 – the unofficial holiday of marijuana – culminating in a synchronized smoke at 4:20pm.

Held on April 20 annually, the digits 4/20 have become synonymous with cannabis culture, as the date is written in the North American calendar as 4/20.

In Canada, it’s the end of an era in some ways, as this will be the last celebration before marijuana is set to become legal. Last year, an estimated 40,000 people attended Vancouver’s 4/20 celebration, with even more expected this year.

Why did 4/20 become synonymous with marijuana?

Reportedly, the term originated in northern California in the 1970s, as five students at San Rafael High School would meet at 4:20pm to smoke marijuana. 

‘‘We thought it was a joke then,’’ said David Reddix, a filmmaker and retired CNN cameraman, told the Associated Press. ‘‘We still do.’’

These days, it’s gone mainstream, with 4:20pm being weed’s equivalent of happy hour.  

Vancouver famous for its blazing annual event

Vancouver is famous for its annual 4/20 event, which started in Vancouver in 1995, led by Marc Emery, the self-titled “prince of pot” as a protest calling for the legalisation of cannabis.

But this year, the celebration of cannabis culture might feel slightly different — it will most likely be the last one before recreational marijuana use becomes legal.

However, advocates say they are still other things left to fight for:

Dana Larsen, Vancouver’s 4/20 organizer says the annual smoke-ups will continue and cannabis users are still face discrimination.

“I wouldn’t say we’re above the law,” Larsen told Canada’s Globe and Mail newspaper. “I’d say we’re under the law, in that cannabis users are unjustly punished by the law, and imprisoned, and treated poorly, and lose our jobs, and our children, and have other negative things happen because we choose to use cannabis, often instead of using alcohol."