April 20th is ”420.”
“420” is an American or Canadian slang term for marijuana.
This day is called marijuana day, as every year on April 20th, there are marijuana events in various parts of these countries.
It’s not clear why it’s ”420”, but it’s said to be:
A long time ago, a group of high school students from San Rafael, California, gathered at 4:20 pm every day to smoke cannabis.