A red giant is an ageing star swollen to vast size, read as a late, expansive stage of something. Dream books connect it to maturity, and to a situation growing larger as it nears its end.
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.