Where did the Phrase "flea market" originate and why?

Answer 1

The original flea market is likely to be the Marché aux puces of Saint-Ouen, Seine-Saint-Denis, in the northern suburbs of Paris. It is a large, long-established outdoor bazaar, one of four in Paris. They earned their name from the flea-infested clothing and rags sold there.

Answer 2

Here are some sites that list some theories:

http://ididnotknowthatyesterday.blogspot.com/2006/03/where-did-term-flea-market-come-from.html
http://en.wikipedia.org/wiki/Flea_market