"急板之乐曲或乐章" can be translated into English as "a musical piece or movement in prestissimo tempo".
Here, "prestissimo" is the musical term for an extremely fast tempo, often used to describe the quickest possible pace in music. While "急板" in Chinese directly refers to a very fast tempo, "prestissimo" is the closest and most commonly used equivalent in Western musical terminology. The phrase "a musical piece or movement in prestissimo tempo" clearly conveys the idea of a composition or section thereof characterized by such a rapid pace.