As in a town square market, as seen in human culture for the last few thousand years.

For non-native speakers, market has a specific meaning in US English. In the US a “market” typically means a small shop selling the most common fruits, vegetables, snacks, and household items.

In Europe a market is a larger and more general area for autonomous small traders, usually also trading food and household goods.

The autonomy and low barrier to entry make them a good analogy to a stock market.

(They also suffer from availability and quality issues. A large business can arrange to purchase and retail all of these goods on behalf of consumers under one roof — a supermarket.)