Devotees of Maa Durga across the world are celebrating navratri festival, that goes on till Oct. 10 this year. Maa Katyayani is the sixth form of Maa Durga. So the sixth day of Navratri is dedicated to her. 
Goddess Durga took the form of  Katyayani to destroy demon Mahishasura. It was the most violent form of Goddess Parvati. In this form, Parvati is also known as the Warrior Goddess. Legend has it that she was born as the daughter of Sage Katya of Katya clan, after he performed hard penance of Maa Bhagvati.