The word Antichrist means = One who opposes Christ, or who puts himself in the place of Christ, a false Christ.
In the Scriptures we find 2 main concepts of Antichrist:
1 / A spirit – That operates in false believers, heretics, etc. who oppose Jesus Christ Divinity, His teachings, etc. (1 John 2: 22-23, 2 Jn.1:7) and of these kind there are many in the world. But also there are some men who usurp Christ’s place and who call themselves saviors, messiahs, etc. So they operate under the influence of this spirit of antichrist.
2 / A man – The bible also speaks of a particular man coming, the man of sin, the son of perdition, that by Satan’s works at the end of times, will make great signs and that will oppose Jesus Christ teachings and put himself in Christ’s place, deceiving many.