Dreams are both pleasant and unpleasant or nightmarish.
Sometimes a dream is based on truth and foreshadows a coming event. The significance of such a dream is realised at a moment when our vision flows into a real occurrence. Coming to the meaning of this Hadith, since the institution of Prophethood is abolished, Revelation too cannot descend upon anybody. Yet, one Prophetic vestige still exists and that means a prophetic dream about some future event. It may be with a good or bad omen, though this Hadith brings into focus dreams with good tidings alone.