If you have two Jews in the room, you’ll get three definitions of Klezmer. So what follows is at best a “mishmash” of Klezmer definitions.
Klezmer is a Yiddish word that comes from the Hebrew words klei and zemer, meaning, basically, musical instruments. Around the 15th century, a tradition of secular (non-liturgical) Jewish music was developed by musicians with a repertoire largely made up of dance songs for weddings and other celebrations. Due to the Ashkenazi lineage of this music (i.e., Jews from Central and Eastern Europe, as opposed to Spain or Portugal), the lyrics, terminology and song titles are typically in Yiddish (Jews from Spain and Portugal spoke Ladino rather than Yiddish). Since klezmorim (players of Klezmer) were often hired to play non-Jewish functions, and non-Jewish musicians sometimes played Jewish events, klezmer music became a fairly eclectic mix of Eastern European folk styles.
A pure klezmer band has no vocalist – on the contrary, Klezmer music is intended itself to replicate the human voice, including sounds of crying, wailing and laughing. But most klezmer bands these days alternate vocals with musical interludes. Klezmorim create a motion and feel that doesn’t fit easily into 4/4 time. It’s no accident that when Jewish musicians abandoned the “old world” music and moved into the American idiom, many of them (most notably Benny Goodman) moved into jazz.
There are klezmer modalities and ways of dealing with improvisation that help the ear notice what is klezmer. A major element is the prevalence of minor keys, and the “krechts,” or soulful burst of intensity that the lead musician, often a clarinet, will play, almost like an instrumental complaint.
Or, putting it succinctly, as some describe it, Klezmer is “deedle deedle deedle music.”
See for yourself, with Itzhak Perlman playing Klezmer (his solo starts at 1:44 minutes):
