Top Definition
A group of people who ride bicycles together while obeying traffic laws, and showing common polite behavior for roadway travel. Similar to "critical mass", only with a positive attitude, pleasant phrases, and very little spitting. Examples include the Bike Party in San Jose, CA, and the Maroon Bike Project Courteous Mass in College Station, TX, and many other polite group bicycle rides in other cities.
Bicyclist: "Hello there! We'll be coming down the road on your right side. Thank you for noticing us. Happy Friday! It's Courteous Mass!"

Motorist: "Hello! Happy Friday to you too! What a nice group of people riding bicycles together. Such a lovely activity! I'll gladly share the public road with them anytime!"
by orangek July 21, 2011

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