Maa Kalratri is the seventh form of the nine forms of Goddess Durga also known as Kali. Kaal means time and death and Kaalratri means the One who is the Death of Kaal.
Goddess Kaalratri is widely regarded as one of the many destructive forms of Mother Goddess - Kali, Mahakali, Bhadrakali, Bhairavi, Mrityu, Rudrani, Chamunda, Chandi and Durga.
Kalaratri is the one who destroys ignorance and removes darkness. This form primarily depicts that life also has dark side – the violent Mother Nature who nurtures life can also create havoc and remove all dirt. The Goddes is also known as Shubhankari.
Kaalratri Mantra:
Om Bhurbhuva svah kalaraatri iha gaccha ihatisha
kalaratryai namah kalaratrimavahayami sthapayami
namah padhyadibhih pujanaambidhaaya
Also See: Navratri 2017, Day 7: Know about Maa Kalratri's Interesting fact