In 1979 the Society for Biblical Literature offered this definition:

" 'Apocalypse' is a genre of revelatory literature with a narrative framework,
in which a revelation is mediated  by an otherworldly being  to a human recipient,
disclosing a transcendent reality which is
both temporal, insofar as it envisages eschatological salvation,
and spatial insofar as it involves another, supernatural world."

Writings in the Bible that qualify as apocalyptic or close to it include:

Daniel 7-12
Zecharian 9-14
Ezekiel 38-39
Isaiah 24-27

and, of course The Book of Revelation