Query: What is part of the time between Passover and Shavuot thought to be?
Context: During the Three Weeks musical instruments are prohibited. Many Jews consider a portion of the 49-day period of the counting of the omer between Passover and Shavuot to be a time of semi-mourning and instrumental music is not allowed during that time. This has led to a tradition of a cappella singing sometimes known as sefirah music.