The ability to express and act in a manner without restriction of rules or oppression. Until mankind can co-create its own kingdom of heaven on this Earth, there will always be rules and oppression.
To understand another picture of freedom, consider a fly that is trapped by a spider. One might consider that the fly is a prisoner. Yet, it is the fly who is free to experience pleasure and danger, while the spider is confined to its own web. This forms an interesting thought to meditate upon, relative to our own states of existence.