Starting from Tuesday night, April 6th, we count 49 days between the first day of Pesah to Shavouot. The Rambam explained the counting of these days as equivalent to one who patiently awaits a beloved friend. Every day passes with hope and anticipation as the arrival draws near.
In later centuries, a note of sadness was attached to these days. Tradition tells us of an adversity that befell the students of Rabbi Aqiva during the counting of the Omer. History also records the appalling massacres of Jews during this time by the Crusaders in 1096. Therefore, this period has become a period of semi-mourning, in which Jews abstain from weddings and rejoicing until the 33rd day of the Omer.