noun
Refers to the most memorable, climactic part of a song, often repeated. In J-pop and similar contexts, it typically corresponds to the chorus, but can also mean a catchy instrumental or vocal hook.
この曲のサビはすぐ覚えられる。
The hook of this song is easy to remember right away.
サビの部分でみんな一緒に歌った。
Everyone sang along during the chorus.
From the noun 錆 (さび, 'rust'), possibly via the idea of a 'rusty' or rough vocal quality in traditional music, or from the verb 寂びる (さびる, 'to become mellow/patina'). The exact derivation is uncertain.