The Mark of the Beast mean in Revelation?

The mark of the beast does not exist yet.

The mark of the beast is some kind of seal that followers of the Antichrist will take in allegiance to him. The prophecy of Revelation 13:16–17 says that the image of the beast “forced all people, great and small, rich and poor, free and slave, to receive a mark on their right hands or on their foreheads, so that they could not buy or sell unless they had the mark, which is the name of the beast or the number of its name.”

We don’t know what this mark will look like. A while ago, some thought it was a stamp or tattoo of the number 666. More recently, people thought it might be a bar code. Now a popular speculation is that the mark of the beast will be an implanted microchip that allows people to access their digital currency. But we honestly have no way of knowing what form the mark of the beast will take.

All that matters is that we take a stand NOW for whom we will serve, before the Antichrist is identified.

Poorly written fiction

It means John ate some mushrooms he probably shouldn't have.

It is the number of a man - the Antichrist. The number is given as 666.