Leil Selichot
Begins after nightfall on Saturday, 12 September 2020 (23rd of Elul, 5780)
Selichot or slichot (Hebrew: סליחות) are Jewish penitential poems and prayers, especially those said in the period leading up to the High Holidays, and on Fast Days. In the Ashkenazic tradition, it begins on the Saturday night before Rosh Hashanah. If, however, the first day of Rosh Hashanah falls on Monday or Tuesday, Selichot are said beginning the Saturday night prior to ensure that Selichot are recited at least four times.
Source hebcal