An apple that looks fine outside but hides a worm is read as a hidden flaw or doubt within something attractive. Dream tradition sees it as a nudge to look a little closer.
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.