In reference to the bicycle critical mass, the name stems from what happens at busy intersections in large cities. Many car drivers (I'm speaking from experience) are too air headed to yield to a bicycle which might have the right of way. This causes many people to end up loitering at an intersection waiting for a chance to cross on their bikes. When the bicyclists reach "critical mass" there is enough of them to cause a large enough controlling force (or distraction from a driver wanking) to where they may cross. This term was first coined in a documentary in support of the bike (and other topics), "Return of the Scorcher" by Ted White.