This term does not originate from within the channel, but it is used enough by channelers that people will occasionally ask me about it. Despite having been in an LTR where I should have known this term, I actually only learned it in the summer of 2000, long after said relationship had ended. 4:20 is a time of day, but specifically, it has significance to pot smokers. It is said to have been derived from "420," the now-defunct San Rafael Police Department radio code for "marijuana smoking in progress". At twenty minutes past four (usually in the afternoon, but it could just as easily be in the wee hours of the morning), pot smokers the world over (or at least in any given time zone) light up in a kind of one-world-one-bong kind of thing.