what does 420 mean

How did 420 spread from a circle of California stoners across the globe?
What's so special about 4/20? It has long been debated as to why April 20, the unofficial holiday of the Marijuana enthusiast
The bands that Patrick managed for Lesh were called Too Loose To Truck and the Sea Stones; they featured not only Lesh but
The origin of the term 420, celebrated around the world by pot smokers every April 20th, has long been obscured by the clouded memories of the folks who made it a phenomenon.