What is "mastani"

Mastani was the second wife of the Maratha Peshwa Bajirao I. She is said to have been a beautiful and brave woman, skilled in arts, literature, and warfare. She had been dearly loved by Peshwa Bajirao but always neglected by his mother Radhabai and his brother Chimajiappa. However, she was treated with kindness by Bajirao's first wife Kashibai.