Sankrant

Sankranti (Sanskrit: संक्रान्ति saṁkrānti) means transmigration of the Sun from one Rāshi (constellation of the zodiac in Indian astronomy) to the next. Hence, there are 12 Sankrantis in a year.

Each Sankranti is marked as the beginning of a month in the sidereal solar calendars followed in Andhra Pradesh, Telangana, Karnataka, Maharashtra, Kerala, Odisha, Punjab, Gujarat & Nepal . On the other hand, in the sidereal solar Bengali calendar and Assamese calendar, a Sankranti is marked as the end of each month and the day following as the beginning of a new month.

...
Wikipedia