Which of the following indicates a gradual increase in speed?

The term that indicates a gradual increase in speed is "accelerando." In musical terminology, "accelerando" instructs performers to gradually increase their tempo, creating a sense of forward momentum and excitement in the music. This technique is often used to heighten emotional intensity as a piece progresses, leading to climactic moments.

In contrast, "ritardando" refers to a gradual decrease in speed, allowing the music to slow down and create a reflective or dramatic effect. "Crescendo" pertains to a gradual increase in volume rather than speed, used to amplify the dynamic level of the music. Lastly, "legato" describes a smooth and connected style of playing or singing, focusing on the way notes are articulated rather than the tempo of the piece. Understanding these terms enhances musical interpretation and allows for appropriate expression in performance.