A klezmer jam is a gathering of musicians to learn tunes while they are played and to experience playing with other musicians. A leader guides the choice of tunes and their tempos, keeping the musicians together and moving on to another tune after sufficient repetitions of the previous one. Once the session is moving along, other players call out tunes they would like to play.
See WHAT IS A JAM SESSION? — by Stuart Brotman

A slow jam is a klezmer jam in which tunes are played by ear, but much more slowly than usual. Sometimes this is accompanied by teaching of some songs (call and response).
See WHAT IS A SLOW JAM? — by Stuart Brotman

A klezmer instrumental workshop is a gathering in which participants learn klezmer tunes and techniques from a teacher, sometimes with the use of musical charts. There is ample time for repetition and discussion.

A KlezCalifornia Yiddish sing-along is a get-together to sing Yiddish songs, relying on the KlezCalifornia SongBook or on song sheets provided by participants. Specific songs are chosen by a leader or by participants.

Learning by ear rather than from written music has specific benefits.
See WHY WE LEARN BY EAR — by Joshua Horowitz