Something in your life is not what it seems. Perhaps a misunderstanding on your part, or a truth you cannot admit to yourself. It may also indicate something important being kept from you by another. This may be a source of worry or depression in your life, and the Moon is a strong indicator that you must rely on your intuition to see through the deceit.
To get the full traditional meaning and interpreation of The Moon, I suggest you visit Trusted Tarot and their The Moon page.