A holiday self established by marijuana smokers that takes place on April 20th.
Originally started by a group of college kids who would meet at a statue everyday at 4:20 PM to smoke weed.
Some other drug usage may take place but marijuana is the main one.
Pronounced "four twenty", if you say, "four hundred twenty" you'll look like an idiot.
Me: My dad got so baked yesterday.
Me: It was 4/20.