An enemy combatant is distinguished from a prisoner of war. Under current American law, an enemy combatant is not afforded the same rights as a prisoner of war.
The term is especially significant in the context of terrorism; if a person is captured in connection with terrorism, they are often defined as an enemy combatant.
Enemy combatant is a relatively new term in American military law. Under the traditional rules of war, enemy soldiers captured as lawful combatants or prisoners of war are afforded specific rights and protections in American custody. Lawful combatants are those operating under a recognized and organized command structure, wearing official uniforms and openly carrying arms.
With the rise of terrorism, American law treats operatives who do not meet the definition of lawful combatant as enemy combatants who possess fewer rights and protections in American custody.