what is allegro music
2. a musical composition or passage performed quickly in a brisk lively manner. Familiarity information: ALLEGRO used as a noun is rare. â¢ ALLEGRO (adjective). The adjective ALLEGRO has 1 sense: 1. (of tempo) fast. Familiarity information: ALLEGRO used as an adjective is very rare. â¢ ALLEGRO (adverb). The adverb ALLEGRO has 1 sense: 1. in a quick and lively tempo. Familiarity information: ALLEGRO used as an adverb is very rare.