Friday is the 26th day, which is three 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 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.
Former Chief Rabbi Mordecahi Eliahu has stated that it is permissible during the Omer counting period to make a festive engagement, Brit Mila, or Pidyon HaBen meal, even if friends are invited, on the condition that it is a meal alone and without dancing and without the playing of music instruments. It is permissible only to sing and praise the Almighty vocally.
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 during the Bar Kochba uprising.