This card is both a portent of celebration and cause for it. It tells of great happiness in the future for you, and not of the passing kind, but secure joy which will last and be shared with those around you. Commonly associated with the completion of a meaningful project, or, even more likely, a birth.
To get the full traditional meaning and interpreation of Three Of Cups, I suggest you visit Trusted Tarot and their Three Of Cups page.
