Jam session | (Abbreviation: jam) An informal, improvized performance with a group of musicians, originally applied to jazz; the term is an acronym for ‘jazz after midnight.’
Jazz | An eclectic musical style that emerged in the early twentieth century that features improvisation, syncopation, and usually a regular or forceful rhythm. Brass and woodwind instruments and piano are typically used, although guitar and occasionally violin are also used; styles include Dixieland, swing, bebop, and free jazz.
Jazz band | An instrumental ensemble that plays jazz music, usually without a conductor; typically includes reed (saxophones and clarinets), brass (trumpets and trombones), and rhythm sections (percussion, piano, double bass, and sometimes guitar).
Jazz chart | (See chord chart.)
Jew’s harp | A small, lyre-shaped instrument held between the teeth and struck with a finger; produces only one note, but its sound changes when the player alters the shape of the mouth cavity.
Jig | A vigorous dance (and style of music) developed in the British Isles, usually in compound meter; still popular as a traditional Irish genre.
Jingle | A short, memorable piece of music (often only a few seconds long) used to identify a radio station or to promote a product.