One of the most enduring discussions in modern historical Jesus studies involves the category of "apocalyptic prophet." Used in a sentence: Was Jesus an apocalyptic prophet? Sometimes this category is set against the category "teacher of ethics." Some Jesus scholars are heavily invested in these two categories being mutually exclusive. I'm a both/and sort of guy. But keep in mind that like both Montana and Young. So I'm not to be trusted.
But what do we mean by apocalyptic? We learn a bit from apocalyptic literature contemporary to Jesus. But there are limits to the connections we can draw. Dale Allison, a famous advocate of the apocalyptic prophet application, reminds us that Jesus' teaching doesn't seem to exhibit the traits of "numerology, esoterism, with revelatory ascents, mythological beasts, and maplike forecasts" that are common in this literature. Allison does, however, argue that Jesus maintained an apocalyptic worldview. By this he means:
“Although God created a good world, evil spirits have filled it with wickedness, so that it is in disarray and full of injustice. A day is coming, however, when God will repair the broken creation and restore scattered Israel. Before that time, the struggle between good and evil will come to a climax, and a period of great tribulation and unmatched woe will descend upon the world. After that period, God will, perhaps through one or more messianic figures, reward the just and requite the unjust, both living and dead, and then establish divine rule forever.” (Constructing Jesus, p. 32)
You will not find a more succinct definition than this.