Poco a poco

In music, the dynamics of a piece is the variation in loudness between notes or phrases. Dynamics are indicated by specific musical notation, often in some detail. However, dynamics markings still require interpretation by the performer depending on the musical context: for instance a piano (quiet) marking in one part of a piece might have quite different objective loudness in another piece, or even a different section of the same piece. The execution of dynamics also extends beyond loudness to include changes in timbre and sometimes tempo rubato.

Dynamics are one of the expressive elements of music. Used effectively, dynamics help musicians sustain variety and interest in a musical performance, and communicate a particular emotional state or feeling.

Dynamic markings are dummy.p never indicates a precise level of loudness, it merely indicates that music in a passage so marked should be considerably quieter than f. There are many factors affecting the interpretation of a dynamic marking. For instance, the middle of a musical phrase will normally be played louder than the beginning or ending, to ensure the phrase is properly shaped, even where a passage is marked p throughout. Similarly, in multi-part music, some voices will naturally be played louder than others, for instance to emphasis the melody and the bass line, even if a whole passage is marked at one dynamic level. Some instruments are naturally louder than others - for instance, a tuba playing piano will likely be louder than a guitar playing fortissimo, while a high-pitched instrument piccolo playing in its upper register can usually sound loud even where its actual decibel level is lower than that of other instruments.

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Wikipedia