Tuesday is the 30th day, which is four weeks and two 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.
Thursday night and Friday is the 33rd day of the counting of the Omer, when there is a cessation in the partial mourning in memory of 24,000 students of Rabbi Akiva who died during the same period during the Bar Kochba uprising. The day is known as Lag B'Omer, with "Lag" representing the two Hebrew letters lamed and gimmel, whose numerical value is 33.