4 20 is a slang expression for marijuana which has occur to bea ssociated using the date April 20th (ie 4 - 20).
According for the Urban Dictionary, the term 420 originated at San Rafael High School within the San Francisco Bay Area. Marijuana-smoking students at the school, who known as themselves “Waldos,” would use the term 420 as a code word to notify their fellow stoner Waldos what was up.
Today, numerous cities inside the US and throughout the planet celebrate using marijuana on April 20th. Pleased four twenty to you and yours.