The eighth night of Navratri is known as Durgashtami. It commemorates the day on which Goddess Durga gained victory over the demon Maheshasura.
Seventh night of Navratri Worship Kalaratri
Kalaratri is the NavDurga whom we worship on the 7th night of Navratri. She is the most fierce of the 9 goddess and teaches us to follow our true path.