Rosh Hashanah is Jewish New Year and, in 2023, it is celebrated from the evening of Friday 15 September for two days. The name 'Rosh Hashanah' does not appear in the Torah, where the corresponding term is 'Yom Teruah' (day of shouting). In ancient times, it is quite likely that it was not considered to be the start of a new year and, instead, it marked messengers going around Israel to tell people that the important pilgrimage festival of Sukkot was just 14 days away.
However, for most Jews (Samaritans and Karaites still celebrate Yom Teruah), Rosh Hashanah (literally 'head of the year') has come to signify a new start and a new year. It is the day on which G-d opens the Book of Life to decide who is to be blessed with life over the following year, and is a time to both forgive others and to seek forgiveness.