Hebrew: סְפִירַת הָעוֹמֶר, Sefirat HaOmer
The omer ("sheaf") is an old Biblical measure of volume of unthreshed stalks of grain, the amount of grain used for the Temple offering.
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".[1] 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. The Temple sacrifices have not been offered since the destruction of the Temple in Jerusalem, 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 period of the counting of the Omer is considered to be a time of potential for inner growth—for a person to work on one's good characteristics (middot) through reflection and development of one aspect each day for the 49 days of the counting.
In Kabbalah, each of the seven weeks of the Omer-counting is associated with one of the seven lower sefirot (Chesed, Gevurah, Tiferet, Netzach, Hod, Yesod, Malkuth). Similarly, each day of each week is associated with one of these same seven sefirot, creating forty-nine permutations. The first day of the Omer is therefore associated with "chesed that is in chesed" (loving kindness within loving kindness), the second day with "gevurah that is in chesed" (might within loving kindness); the first day of the second week is associated with "chesed that is in gevurah" (loving-kindness within might), the second day of the second week with "gevurah that is in gevurah" (might within might), and so on.