Excerpted from The Jewish Religion: A Companion (Oxford University Press).
The Omer (“sheaf”) was a harvest offering brought to the Temple on the second day of Passover (Leviticus 23:9-14). There is a further command that, from the day when the Omer was brought, seven weeks were to be counted, and on the 50th day a festival was to be celebrated (Leviticus 23: 15-21). This festival was later called Shavuot, “the Feast of Weeks” because it falls on the day after the seven weeks have been counted.
In the Rabbinic tradition, all this was understood to mean that, even after the destruction of the Temple, each individual should actually count these days, by saying each day, “This is the X day of the Omer.” Among the many interpretations given to counting the Omer is that Shavuot celebrates the giving of the Torah while Passover celebrates the Exodus from Egypt. The free man, as he reminds himself of the bondage in Egypt, counts each day towards the even greater freedom enjoyed by those who live by the Torah.
In the Middle Ages, the Omer period became one of sadness and mourning. Various conjectures have been made about why what was presumably a joyous period in Temple times was transformed in this way. Traditionally, Jews do not have a haircut during this period, and weddings do not take place. There are, however, different customs regarding the duration of the mourning period. Some observe it from the end of Passover to Lag Ba-Omer (the 33rd day), others from the end of Passover until Shavuot or until three days before Shavuot, and there are other variations.
In the kabbalah [Jewish mysticism] each of the 49 days of the Omer represents one of the combinations of the seven lower Sefirot (divine emanations, i.e., in each one there are all seven) and in a kabbalistic prayer the worshipper entreats God to help him [or her] lead pure life and pardon him [or her] for the flaw he [or she] has produced in the Sefirah of the day.
Pronounced: shah-voo-OTE (oo as in boot), also shah-VOO-us, Origin: Hebrew, the holiday celebrating the giving of the Torah at Mount Sinai, falls in the Hebrew month Sivan, which usually coincides with May or June.
Pronunced: TORE-uh, Origin: Hebrew, the Five Books of Moses.