Antichrist is a term used in Christian theology [the study of Christian beliefs and teachings] to refer to a person who is believed to be an opponent of Jesus Christ.
For example, in the Bible, the Antichrist is described as a figure who will spread evil and deceive people, opposing the teachings of Jesus Christ.
Very Simple Definition:
Antichrist is a word used to describe someone who goes against Jesus in an evil way. For example, in stories, the Antichrist is a bad person who tries to do bad things and doesn’t follow Jesus.