noun
dream that goes against reality; dream that predicts the opposite
Refers to a dream whose content is contradicted by actual events, often used in the context of dream interpretation where a dream is believed to foretell the opposite of what will happen.
試験に落ちる夢を見たけど、逆夢だったみたいで合格した。
I dreamed I failed the exam, but it seems it was a dream that predicted the opposite, and I passed.
宝くじが当たる夢を見たが、逆夢で当たらなかった。
I dreamed I won the lottery, but it was a dream that went against reality and I didn't win.