A Seal Upon Him
(Rev. 20:3 KJV) 3 And cast him into the bottomless pit, and shut him up, and set a seal upon him, that he should deceive the nations no more, till the thousand years should be fulfilled: and after that he must be loosed a little season.
Satan is cast into prison and the door is locked and sealed. The seal shows that he can’t open the door because it’s by God’s authority that he’s bound. He can’t deceive the nations until the end of the 1000 years.
A Thousand Years
(Rev. 20:2 KJV) 2 And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years,
The 1000 years is the millennium kingdom. Some believe the wording is figurative and just means a very long period of time.