Overview
The term open market is used generally to refer to an economic situation close to free trade. In a more specific, technical sense, the term refers to interbank trade in securities.
In economic theory
Economists judge the "openness" of markets according to the amount of government regulation of those markets, the scope for competition, and the absence or presence of local cultural customs which get in the way of trade. In principle, a fully open market is a completely free market in which all economic actors can trade without any external constraint. In reality, few markets exist which are open to that extent, since they usually cannot operate without an enforceable legal framework for trade which guarantees security of property, the fulfillment of contractual obligations associated with transactions, and the prevention of cheating.
A physical open market is a space where anyone wishing to trade physical goods may do so free of selling charges and taxes, and has come to be regarded by many activists as the ultimate social enterprise and a major tool for tackling unemployment.
From Wikipedia (CC BY-SA 4.0).