Thursday is the 46th day, which is six weeks and four days of the counting of the Omer, the measure of barley that was harvested in ancient times at the beginning of the 49-day counting period and brought to the Holy Temple as a sacrifice. The end of the counting period coincides with the evening before Shavuot, the festival of the first fruits that also marks the handing down of the Torah on Har (Mount) Sinai. The blessing over the counting of the Omer is recited at night and is omitted during the day if one forgot to count.
Shavuot, the Festival of Weeks, is the second of the three major festivals with both historical and agricultural significance. Agriculturally, it commemorates the time when the first fruits were harvested and brought to the Temple, and is known as Chag HaBikurim (the Festival of the First Fruits). Historically, it celebrates the giving of the Torah at Mount Sinai, and is also known as Chag Matan Torah (the Festival of the Giving of the Torah).