noun
Refers to an orchestral opening piece, or metaphorically to an event that signals the beginning of something larger.
オーケストラがオペラの序曲を演奏し始めた。
The orchestra began to play the opera's overture.
この小さな衝突は、後に続く大戦争の序曲に過ぎ
This small clash was merely a prelude to the great war that followed.
Compound of 序 (jo, 'beginning' or 'order') and 曲 (kyoku, 'musical piece'). The word is a direct adaptation of the Western musical concept of an overture.