The anus is read as release, control and letting go of what is no longer needed. Dream books link it to holding on too tightly or finally releasing.
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.