Monday is the eighth day, which is one week and one day, of the counting of the Omer, the measure of barley that was harvested in ancient times at the end of the 49-day counting period. The first crops were offered as a sacrifice in the Holy Temple. The blessing over the counting of the Omer is recited at night and is omitted during the day if one forgot to count.
The period of counting culminates the night before the festival of Shavuot (Pentecost), when Jews celebrate the giving of the Torah on Har Sinai (Mount Sinai).