Jewish calendar has 2 different meanings across 2 categories:
(Judaism) the calendar used by the Jews; dates from 3761 BC (the assumed date of the Creation of the world); a lunar year of 354 days is adjusted to the solar year by periodic leap years
The annual calendar used in Judaism. It determines the Jewish holidays, which Torah portions to read, yahrzeits (Yiddish: yortsaytn), and which set of Psalms should be read each day.