Final answer:
A command economy is a system where the government controls all aspects of economic activity, contrary to a market economy which is decentralized and based on supply and demand.
Step-by-step explanation:
A command economy is best described as a system where the government controls all aspects of economic activity. In a command economy, the government determines what to produce, how to produce it, and who receives the goods or services. This is in contrast to a market economy, where economic decisions are decentralized and based on supply and demand.