Honestly, How do you know, you are not a slave?
I know “The best way to keep a prisoner from escaping is to make sure he never knows he’s in prison.”
― Fyodor Dostoyevsky
TL;DR
Free, in all cases, means not moved or forced, without any feeling of constraint: the mere fact of being able to make one's own life an experiment, without any authorization from any man, institution or government.