Which term indicates a dramatic or sudden change in tempo?

The term that indicates a dramatic or sudden change in tempo is "agitato." This term is often used to convey a sense of agitation or excitement in the music, leading performers to interpret the passage with a heightened emotional intensity, often resulting in an abrupt change or emphasis on tempo. While "accelerando" refers to a gradual increase in speed and "allargando" suggests a gradual slowing down, "agitato" captures the essence of a marked or sudden shift in the pacing, aligning with the dramatic effect sought by the composer. "Ad libitum," on the other hand, allows for flexibility with tempo, but does not specifically indicate a dramatic change.