In Chinese thought yin and yang are opposites that complete each other, each holding a seed of the other. A dream of the sign is read as a call for balance between rest and action, softness and strength.
Where in your waking life have you met something like this lately?
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.