free: belonging to no master and bound by no claim, whether in legal standing (not a slave) or in relation to a law, tie, or power
In the world of the New Testament, being free was first of all a social fact. A person was either free or a slave, and everyone knew which. So the word usually appears paired with its opposite, slave or free, over and over, as a way of naming every kind of person without exception.
The New Testament then stretches that everyday word. It can narrow to a single tie a person is released from: a son exempt from a tax, a widow free to remarry, a teacher who owes no one. Paul even builds a whole picture on it, casting Sarah as the free woman and Hagar as the slave, so that being free stands for the promise while slavery stands for bondage.
Deepest of all is the freedom that has nothing to do with legal status. A person can be legally free and still enslaved to sin, or legally a slave and yet truly free in Christ. When the Son sets someone free, they are free indeed, and that is a freedom no earthly master can grant or take away.