A parallel world is read as the lives you did not live — other choices playing out. Tradition sees it as reflection on decisions and on the many versions of the self.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.