A market economy system is characterized by privately owned means of production.
In a market economy the economic agents own the factors of production and are free to offer them in the factor markets in exchange for a retribution.
In this system, the prices and the quantities exchanged are decided in the markets, after the interactions of the aggregate desires of all consumers and producers. There are almost no interventions from the goverment.
On the other hand, a centrally-planned economy would be a system in which the means of production are collectively owned by the whole society, and therefore, are in hands of the public authorities.
