when the thousand years have expired, Satan will be released from his prison
Will be released is λυθήσεται [lythēsetai] : to set free prisoners.1 Satan was bound and imprisoned in the abyss and is now set free. Prison is φυλακῆς [phylakēs] , the same word which indicated the imprisonment of demons in Babylon (Rev. Rev. 18:2+). Contrary to amillennial assertions, during the Millennial Kingdom Satan will not be able to deceive anyone even to the slightest degree. He is not omnipresent and spends the entire time locked away in the abyss. See commentary on Revelation 20:2.
1 Frederick William Danker and Walter Bauer, A Greek-English Lexicon of the New Testament and Other Early Christian Literature (Chicago, IL: University of Chicago Press, 2000), 483.