Dhanteras is the first day of the 5 day Diwali Festival as celebrated in parts of north India. The festival, known as "Dhanatrayodashi" or "Dhanvantari Trayodashi".
The word Dhan means wealth and Teras means 13th day as per Hindu calendar. It is celebrated on the thirteenth lunar day of Krishna paksha (dark fortnight) in the Hindu calendar month of Ashwin.
May you have an auspicious start to the Diwali festivities with Dhanteras!