A free market economy (also called a capitalist or laissez-faire economy) is one in which the government does not directly control what is produced, how it is produced, or for whom it is produced. Instead, these decisions are made by individual consumers and producers interacting through markets.
The mechanism that coordinates all these independent decisions is the price mechanism. Prices act as signals: when consumers want more of a good, demand rises, which pushes the price up. The higher price signals to producers that it is profitable to allocate more resources toward that good. Conversely, when demand falls, prices drop, and producers shift resources away. Through this process of rising and falling prices, resources are automatically directed toward the goods and services that consumers value most.
A state planning committee or a government department would allocate resources in a planned (command) economy, not a free market. Trade unions represent workers' interests and negotiate wages and conditions; they do not determine resource allocation in an economy.
The price mechanism is therefore the defining feature of a free market economy - it allocates scarce resources among competing uses without the need for central direction.