Friday is the 19th day, which is two weeks and five 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.
Most of the days between Passover and Shavuot are a period of partial mourning in memory of 24,000 students of Rabbi Akiva who died during the same period. Haircuts, and dancing are forbidden but were allowed Wednesday night and Thursday, Yom HaAtzmaut (Independence Day).
There are two customs for counting the period in which weddings also are forbidden. One custom is to begin the mourning period from the second night of Passover until Lag B'Omer, and the other custom is to start from the beginning of Iyar until Sivan. Both customs remove the prohibitions on weddings on Lag b'Omer, the 33rd day of the Omer and the day that Rabbi Akiva's students were spared from death.