a cappella - Sung without instrumental accompaniment.
AABA - The most common popular song form.
accent - A note or tone that is given stress by volume or attack.
acid jazz - Music for dancing, first heard in the 1980s, that combines elements of soul jazz, funk, and hip hop, and mixes acoustic and electric instruments. (See also groove and club jazz).
ad lib - Also "ad libitum." A notation on written music that gives the performer freedom to vary the notes or tempo; in jazz it typically means to improvise freely.
air check - A musical radio broadcast that was originally recorded for distribution to other stations; radio broadcasts that people have recorded off the radio that are sometimes released commercially or bootlegged.
all-in - The last chorus (in older jazz), often louder and more vigorous than the rest, and played by the ensemble.
altered chord - A dominant chord that has the 5th or 9th raised or lowered by a single semi-tone.
alternate takes - The various takes recorded of a piece of music at a single recording session, that for whatever reasons were not chosen to be used. (A version recorded on a different day is not an alternate take).
arco - Playing a string instrument with the bow, instead of pizzicato.
arpeggio - Sounding the individual notes of a chord quickly, one at a time, usually starting at the lowest note.
arrangement - An adaptation of a musical composition. Arrangements may be as minimal as a bass line or as complex as a full orchestral score. An arranger may take such great liberties with the original piece that it becomes a new composition.
arranger - A person who writes arrangements.
arrhythmic - Without an obvious beat.
articulation - The style in which a tone is produced, i.e., with slurs, staccato, variations in volume, and the like.
atonal - Without a tonal center.
attack - The manner in which a tone is articulated.
avant-garde jazz - A term loosely applied to various forms of "experimental" jazz first heard in the 1950s, and their later offshoots, especially in the sixties and seventies (see free jazz).
ax - Also "axe." Any musical instrument.