What does 'tempo' indicate in a piece of music?

Tempo refers specifically to the speed at which a piece of music is played. It indicates the pace of the music, often measured in beats per minute (BPM). This is crucial for musicians as it sets the overall mood and energy of the performance; for instance, a fast tempo can create excitement and urgency, while a slow tempo may convey calmness or melancholy. Understanding tempo helps musicians interpret a piece as intended by the composer, ensuring the expressive qualities of the music are faithfully conveyed. Other elements like volume, instrumentation, and key signature play significant roles in music but do not pertain to the speed aspect, distinguishing the concept of tempo as a unique and essential characteristic in music theory.