What term describes the numbers at the beginning of a piece that indicate the number of beats in a measure?

The term that describes the numbers at the beginning of a piece indicating the number of beats in a measure is known as the time signature. The time signature is typically represented as two numbers, one on top of the other. The top number specifies how many beats are in each measure, while the bottom number indicates which type of note receives one beat (for example, a quarter note, eighth note, etc.). This notation is fundamental in music as it provides the rhythmic structure necessary for performing the piece correctly.

In contrast, the other options do not serve the same purpose. The measure refers to the actual section of music that contains a set number of beats, demarcated by barlines. Barlines are vertical lines that separate measures, helping to organize the music visually. Rests denote periods of silence within the music, which do not provide information about the number of beats in a measure. Understanding the time signature is crucial for musicians as it lays the foundation for timing and rhythm in performance.