Coal is read as stored energy, dark on the outside and full of heat within. Folk tradition also gives it a role in new beginnings, and glowing coals stand for passion that lasts.
Has this come up in your dreams before? What was going on in your life then?
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.