Also called Shiva Ratri, the Great Night of Shiva, is a festival in reverence of the god Shiva. The festival is celebrated on the 13th night or 14th day of the waning moon in the Hindu calendar (month of February or March of the English calendar).

Source:

“Calendar of Observances.” Anti-Defamation League, 2019, www.adl.org/education/resources/tools-and-strategies/calendar-of-observances. Accessed 25 Sept. 2020.