According to Hindu mythology, Chamundeshwari is a powerful goddess and an aspect of Devi (Mother Nature). She is another manifestation of Goddess Durga, Parvathi.
She was sent forth from Durga’s head to kill the demons Chanda and Munda. After killing the demons she got the contracted names of the demons, Chamunda. Another story tells Chamundeshwari killed Mahisha, the demon king, after a fierce battle, and hence she is also known as Mahishasuramardini. Chamundi is the fierce form of Goddess Durga and is very similar to Mahakali or Bhadrakali.
She is also referred to as "Devi" (Goddess) or "Shakti" (Energy or Power). It is this energy which helps God to proceed with the work of creation, preservation and destruction. In other words, we say that God is motionless, absolutely changeless, and the Divine Mother Chamundeswari, does everything. Truly speaking, our worship of Shakti reconfirms the scientific theory that energy is imperishable. It cannot be created nor destroyed, it is always there.
During Navarathri, Goddess Chamundeshwaridevi is worshipped for 9 nights with the addition of the last day, Vijayadashami, which is its culmination. On all these ten days, the various forms of Mother Mahisasuramardini (Durga) are worshipped with fervour and devotion. Nine forms of Shakti (Navadurgas) are worshipped, depending on the regional traditions.