In musical notation, crescendo means that the notes are gradually getting louder.

The opposite of crescendo is diminuendo or decrescendo.

Maurice Ravel's orchestral work, Boléro is the world's longest musical crescendo. Beginning quietly, the melody repeats over and over again, gradually increasing in volume for about fifteen minutes.

One of Duke Ellington's longer-form compositions is called Diminuendo and Crescendo in Blue, which also describes the form of the piece.