A flea market is a large, traditionally open-air market where people sell a wide range of goods, typically used. Many communities have weekly versions of these markets which are held in large fields or conference halls during the winter, and some of these markets have been happening for decades, or centuries, in a few cases.
Several different kinds of merchants can be found at a flea market. In some regions, people bring their own possessions to the market, setting up a small stall to sell various used goods. In other cases, a merchant may actually be a dealer of used goods who either frequents these markets or runs a store and travels to them. Used-store owners frequently prowl these events looking for goods which they could resell for a higher price, as well.
It is also possible to find merchants selling new products like handmade jewelry and other crafts at a flea market, and in some areas people sell agricultural products or baked goods as well. Urban areas tend to have very large flea markets due to the bigger population; people in neighboring areas may travel to the site of the flea market in search of deals. The wide variety of sellers makes it impossible to predict the goods for sale at the market.
The name, incidentally, is a reference to flea-laden used clothes which were sold at flea markets in the 17th century. Some people may also call a flea market a bazaar, connecting them with the larger outdoor markets of the Middle East. In some regions, these markets are called trunk or boot sales, since people bring goods for sale in their cars and they may set up stands on their vehicles or in close proximity to them.
It helps to have a good eye when you go to a flea market, as some of the goods are quite excellent, while others are junky. Many people like to have a set goal when they attend the market so that they don't end up with a strange assortment of items that caught their eyes. Going with a goal like a new bicycle or a decent bookshelf is an excellent idea, and it can help you resist the lure of antique tea pots, vintage fruit crates, records, and whatever else might call to you from the cluttered aisles of the market.