Q - What does Millennium mean in the book of Revelation and is it Literal?

A - Millennium Meaning: a thousand years the name given to the era mentioned in Rev. 20:1-7.

Revelation 20:2-3 reports, "And I saw an angel come down from heaven, having the key of the bottomless pit and a great chain in his hand. And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years, 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."

"With Satan bound in the bottomless pit, the beast and the false prophet in the lake of fire, and all the ungodly men and women purged from the earth either at Armageddon or at the judgment of the nations (Matthew 25:31-46), there will be only a "few men and women left" (Isaiah 24:6) still in their natural flesh to enter Christ's millennial kingdom (Matthew 25:34). Redeemed Israel, having been saved both individually and nationally when she sees and accepts her Messiah (Zechariah 12:9-13:1; Romans 11:25,26), will become the world's chief nation. All the ancient prophecies and promises concerning Israel will finally be fulfilled (Isaiah 2:2-4; Ezekiel 37:21-28; Zechariah 9:10; 14:9)."

The “thousand years” or millennium (Greek chiliai), should be taken literally. It is mentioned six times in Revelation 20:2-7, as though the Lord would make it emphatically clear that Satan will be restrained for literally a thousand years. He is certainly not "bound" in this present age, for he still "walketh about, seeking whom he may devour" (1 Peter 5:8).

Peace and righteousness under the iron rule of Christ and His resurrected saints (Revelation 20:4; 2:26,27; 19:15; 1 Corinthians 6:2,3), will endure for a thousand years. Furthermore, the catastrophic changes on the earth's surface during the tribulation judgments will have restored the gentle topography and protecting vapor canopy over the earth (Isaiah 40:4; Psalm 148:4-6), so that the primeval "very good" condition of the whole world (Genesis 1:31) will be restored in large measure. Harmony will also be restored between men and animals, and people will again have only one language and will live to great ages (Isaiah 11:6-9; Zephaniah 3:9; Isaiah 65:20).

The events described in Revelation 20:7-9 take place only after there have been a thousand years of enforced peace and righteousness. In Revelation 20:3, it was said that Satan must be loosed a little season, evidently to give men an opportunity to reveal the basic rebellion still simmering in their human natures, and in order to see openly whether they will choose Satan over God, as their ancestors had done a thousand years before.

Those entering the millennial period will be genuine believers, but their descendants will evidently drift away from the faith of their fathers as the generations accumulate and the population grows. Open rebellion, as well as crime and warfare, will be impossible. Satan and his hosts will all be bound in Hades, but men and women will still be born with sinful natures and will need to receive Christ as their personal Savior by faith. If they do not, they will still be vulnerable to Satanic deception when Satan is released to tempt them.

I was on a web site the other day and this false teacher says that the resurrected dead in Christ and those of us who are alive and are changed into our new glorified bodies will be the people that are living in the new thousand year kingdom of Christ, he said we will have children and repopulate the world with sinless people.

I say this men is a false teacher because what he is teaching goes against the word of God and what it clearly teaches.

Mark 12:24-25
And Jesus answering said unto them, Do ye not therefore err, because ye know not the scriptures, neither the power of God? For when they shall rise from the dead, they neither marry, nor are given in marriage; but are as the angels which are in heaven.

No one will have children after they are changed into their new glorified bodies. We will become Rulers, Kings and Priests.

Only human beings that survive the tribulation and stay true to Christ will have children in the thousand year kingdom of Christ, and they and their children will not be sinless, they will no longer have satin to tempt them but some will still sin against God.