Which of the following best describes 'tempo' in music?

Tempo in music refers specifically to the speed or pace at which a piece of music is performed. It dictates how fast or slow the notes are played, creating a foundation for the rhythm of the piece. Understanding tempo helps musicians and listeners perceive the overall mood and energy of the music. For instance, a faster tempo might evoke excitement or urgency, while a slower tempo could set a more contemplative or relaxed atmosphere.

The other options relate to different musical concepts. Dynamics refer to the volume of the music, affecting how loudly or softly different parts are played. The style of music encompasses the characteristics that define a particular genre or tradition, such as jazz, classical, or rock. The key signature indicates the specific set of pitches or notes used in the piece, which defines its tonal center and can influence its harmonic structure. Therefore, while all these elements contribute to the experience of music, tempo is distinctly about the speed at which the music unfolds.