'Decrescendo' is often represented by which of the following terms?

Decrescendo refers to a gradual decrease in loudness in music. It indicates that the performer should play or sing softer over the course of a passage. This term is commonly denoted in musical notation by the abbreviation "decresc." or by a graphical symbol that visually represents a decrease in volume.

The other terms do not accurately describe what 'decrescendo' means. For example, 'gradually louder' describes an increase in volume, which is the opposite of decrescendo. 'Sorrowful' conveys an emotion without any connection to volume changes. Lastly, 'sweet and soft' may imply softness but does not specifically indicate a gradual change in volume, which is the essential aspect of a decrescendo. Thus, 'gradually getting quieter' is the precise definition of decrescendo, making it the correct choice.