The Omer lasts 49 days from Pesach to Shavuot. A time of sadness, it is relieved on the 33rd day. It recalls the end of a plague in Roman times. Weddings often take place on this day, since they are not usually permitted during the rest of the Omer period.
Picture is a Memorial Tablet and Omer Calendar made of Ceremonial Art-Paper & Parchment dated 1907 by the artist Baruch Zvi Ring, from the Jewish Museum in New York