A variation of the term Chandi, which refers to the Goddess's most powerful and frightening manifestation.
Chandika is one of the Navadurgas, or "nine [forms of the goddess] Durga," who are adored throughout the Navaratri festival's nine nights.
Chandika is the most powerful of these heavenly forms, since she is adored during the festival's ninth and last night.
You may also want to read more about Hinduism here.
Be sure to check out my writings on religion here.