A prophet is someone or thing who predicts the future. For example, many think groundhogs on groundhog day can predict if we will have an early spring.
Some have even decided to replace the groundhog with a prophesying lobster:
Who was the most famous prophet in history? It was probably Jesus, who incorrectly predicted the end of the age/apocalypse would happen in the lifetimes of those hearing him preach, Matthew 24:34; Mark 13:30; and Luke 21:32. (oops)
For a great book for older kids about Jesus as an apocalyptic prophet, see
Jesus: Apocalyptic Prophet of the New Millennium is a 1999 book by New Testament scholar Bart D. Ehrman. In it, he argues that Jesus of Nazareth was an apocalyptic preacher, i.e., his main message was that the end of history was near, that God would shortly intervene to overthrow evil and establish his rule on earth, and that Jesus and his disciples all believed these end time events would occur in their lifetimes. Ehrman also analyses New Testament passages such as Jesus’ supposed birth in Bethlehem of a virgin and finds them not historically credible. (Wiki)