What is the effect of 'Crescendo' on the volume of the music?

Crescendo indicates a gradual increase in volume within a piece of music. This technique creates a dynamic swell that can build excitement, tension, or emphasize a particular moment in the composition. Musicians interpret this directive by smoothly increasing the loudness over a specified duration or passage, as indicated in the score. This gradual change can enhance the emotional impact of the music, contrasting with sudden changes in dynamics.

The other choices do not accurately describe the nature of a crescendo: it does not imply a decrease in volume, a constant volume level, or a sudden stop. Each of those options would lead to a very different expressive quality in the music than what is intended with a crescendo.