1. The subject of a fugue or canon; the first phrase of a musical period.
2. Antecedent and consequent, A pair of musical statements that complement one another in rhythmic symmetry and harmonic balance.

SUGGESTED LISTENING EXAMPLE:

Bach, J.S.: Chromatic Fantasia and Fugue in D minor, BWV 903 (opening)

W. W. Norton - 4-CD Musical Example Bank -- Disc 1, Track 17