Prayers to the Divine Mother
Navaratri means "nava" - nine and "ratri" meaning nights. This is the time of the year when the Divine Mother - Durga Devi - fought the demon Mahishasura for nine nights and triumphed over him by killing him on the ninth nigtht. This story is covered in detail in the Devi Bhagavatam and explains the numerous form that Devi took to destroy different demons.
The deeper symbolism of Navaratri is really where the divine qualities of the Divone Mother oneself. By invoking Her presence and sorshipping Her with an open heart with Love, She helps us to take the next steps on our path home to realisation of the Selfr - that is the Self that is not different from Her.