A due:  Return to unison after divisi.

A niente:  To nothing, e.g. to ppp.

A piacere:  Freedom in performance. Synonymous with ad libitum.

A tempo:  Return to the previous tempo.

Accel., Accelerando:  Gradually becoming faster.

Accelerando, accel:  Gradually faster.

Accent:  Placed above a note to indicate stress or emphasis.

Accidental:  A sharp, flat, or natural not included in the given key.

Accompaniment:  A vocal or instrument part that supports or is background for a solo part.

Ad libitum, ad lib:  A term which permits the performer to vary the tempo and/or to include or omit a vocal or instrumental part. Synonymous with a piacere.

Adagio:  Moderately Slow

Adagio:  Slow; slower than andante, faster than largo.

Addolorato:  Sorrowfully.

Affrettando:  Hurrying.

Agilmente:  Lively.

Agitato:  Agitated; with excitement.

Al coda:  "To the coda."

Al fine:  To the end.

Al segno:  Return to the sign, Dal segno.

Album:  A full length recording. In pop music, it contains a number of songs.

Aleatory, or aleatoric music:  Chance music in which the performers are free to perform their own material and/or their own manner of presentation.

Alla breve:  Cut time; meter in which there are two beats in each measure and a half note receives one beat.

Allargando, allarg:  Slowing of tempo, usually with increasing volume; most frequently occurs toward the end of a piece.

Allegretto:  A little slower than Allegro