A windowpane separates you from the world while letting you see it. Dream tradition reads it as a thin, transparent barrier; a cracked pane as a view of things that has started to change.
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.