Counting of the Omer (Hebrew: סְפִירַת הָעוֹמֶר, Sefirat HaOmer, sometimes abbreviated as Sefira) is a ritual in Judaism. It consists of a verbal counting of each of the 49 days between the holidays of Passover and Shavuot. The period of 49 days is known as the "omer period" or simply as "the omer" or "sefirah".The count has its origins in the biblical command of the Omer offering (or sheaf-offering), which was offered on Passover, and after which 49 days were counted, and the Shavuot holiday was observed. Since the destruction of the Temple in Jerusalem, the Temple sacrifices are no longer offered, but the counting until Shavuot is still performed. Shavuot is the only major Jewish holiday for which no calendar date is specified in the Torah; rather, its date is determined by the omer count.The Counting of the Omer begins on the second day of Passover (the 16th of Nisan) for Rabbinic Jews (Orthodox, Conservative, Reform), and after the weekly Shabbat during Passover for Karaite Jews. According to all practices, the 49-day count ends the day before Shavuot, which is the 'fiftieth day' of the count. The omer ("sheaf") is an old Biblical measure of volume of unthreshed stalks of grain, the amount of grain used for the Temple offering. Source: Wikipedia (en)