A dictionary definition: 1. deliverance; rescue. 2. Theology. deliverance from sin; salvation, atonement for guilt. 3. repurchase, as of something sold. 4. paying off, as of a mortgage, bond, or note.
The common religious definition is usually taken as the 3rd or 4th version above, as though we belonged to another; whereas we have always been God’s, though held in captivity. However, the 1st Century church, and now the most current understanding, is the first definition, in that we have been rescued by a saving conqueror.
In our minds we were held captive (prisoners of war), within the prison of the falsehood of not being in a loving relationship with God, and believed we were less than the image and likeness of God. We have even gone to the extreme of believing we were just products of random evolutionary pondscum. However, on the cross, Christ paid the ultimate price (as in a warfare life sacrifice) to rescue humanity from its delusion (He set the captives free), by defeating the enemy that had propagated ‘The Lie’. (Check out the doctrine of Christus Victor.) Scriptural examples of this include the Exodus of Israel from Egypt and the rescue of the people by Abram after being taken captive by the kings of the valley (Genesis 14:8-16).