What is the term for music gradually becoming louder?

When a piece of music gradually swells in volume, it's employing one of the most powerful tools in a composer's toolkit. This dynamic instruction is known as a crescendo, an Italian musical command derived from the word "crescere," which simply means "to grow." As a fundamental element of musical expression, it directs performers to smoothly increase the intensity of their playing over a series of notes or a longer passage, building energy and anticipation for the listener.

On a written score, a crescendo can be indicated by writing out the abbreviation "cresc." or, more visually, with a symbol called a hairpin that starts at a point and opens to the right (<). The effect is not just about getting louder; it’s a crucial technique for creating emotional arcs within a piece. A slow, steady crescendo can build immense tension and excitement, while a quick one can add a sudden burst of passion.

The direct opposite of this effect is a decrescendo or a diminuendo, which instructs musicians to gradually become quieter and is marked with a closing hairpin symbol (>). Together, these two dynamic markings allow music to breathe, creating a sense of movement and narrative. From the famous, repetitive crescendos of composer Gioachino Rossini to the dramatic swells in a modern film score, this technique is essential for guiding an audience's emotional journey.