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The act of smoking Marijuana, especially at 4:20am or 4:20pm. A play on the police codes for crimes.

Has more significance if smoking at 4:20am or 4:20pm.
Friend: *walks in* Whatcha doin?
Raditude: *holds up bong* Dude, we got a 420 in progress.
Friend: Can I join in?
by Raditude September 28, 2009
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