Thursday is the 18th day, which is two 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 and 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.
Yom HaAtzmaut (Independence Day) provides a break in customs of semi-mourning for 24,000 students of Rabbi Akiva during the same period 2,000 years ago, but weddings are not permitted. The next day that mourning customs are lifted will be the 33rd day of the counting of the Omer, Lag b'Omer, the anniversary of the death of Rabbi Shimon bar Yochai.