The prison is the “bottomless pit,” the earth desolated at the second coming of Christ, where Satan had been confined during the 1000 years (see on v. 1). Satan is to be free to organize the resurrected wicked. This will be his final attempt against God before his destruction.
Loosed.
The confinement resulted from the removal of the righteous to heaven and the slaying of the living wicked (see on v. 2). The loosing will be accomplished by the resurrection of the wicked, which will provide Satan with subjects upon whom to practice his deceptive guile.