• 420 isn't the number of a bill in U.S. Congress to legalize pot, despite many people thinking it is.
• 420 isn't the police or penal code for marijuana possession in California (or any other state), though many people believe that, as well.
• Nor is 420 is the number of chemical compounds in cannabis, the pot plant, though many authors seem fond of stating so.
What 420 is, whether expressed in the form 4:20 (as a time of day), 4/20 (as a calendar date), or just the unadorned numeral (pronounced "four-twenty"), is a universal symbol for the use and appreciation of marijuana. In fact, 4/20 (April 20) has come to be known in certain circles as "Marijuana Appreciation Day."
'420' origin and history
Notwithstanding the many and various urban legends that have grown up about the meaning of "420" and its connection with marijuana, the true story behind it is surprisingly prosaic. In the early 1970s a small group of hippie stoners at San Rafael High School in northern California used to meet at a designated location every day to smoke pot at 4:20 p.m. They did this so regularly that among members of the group "420" became a general euphemism for lighting up.
The catchphrase spread beyond their immediate circle, beyond the high school they attended, and ultimately beyond California, so that within a decade or two pot smokers were using it across the country and indeed the world over.
How popular is the expression today? A Google search on the paired terms "420" and "marijuana" brings up more than 6 million results, including a link to the website of 420 Magazine, a publication dedicated to what it refers to as "cannabis awareness."