a citizen is usually a member of the state or country...so they are entitled to the rights of that state. As a citizen of the US I am entitled to the rights protected in the constitution. a civilian is a person who does not belong to the armed services, Usually this means the military but sometimes it may be used to mean the police. A civilian does not have to be a citizen. As a US citizen, when I visit another country, I am a civilian there but not a citizen.

I am massively tempted to quote Starship Troopers. ;)

civilians is the people whose not in the special force of a government. citizens pertaining to a group of people who live in a certain place.