Allegro, or ALL'O. (I.) Gay, quick. A. term expressive of the third degree of musical rapidity. Generally applied to lively movements ; but sometimes, in conjunction with another word, placed at the beginning of compositions intended to rouse and stimulate the more violent passions ; as allegro agitato, quick and agitated ; allegro furioso, with rapidity and vehemence. Allegro also denotes one of the six distinctions of time, which succeed each other as follows : grave, adagio, largo, vivace, allegro, and presto.