A key signature is a set of sharp or flat symbols placed at the beginning of a musical staff. It indicates which notes are to be played higher or lower than their natural pitches throughout a piece of music. This helps musicians understand the tonal center or key of the composition, making it easier to play and interpret. Key signatures are essential for organizing music into different keys, such as C major, G major, or F major. Each key signature corresponds to a specific scale, guiding musicians on which notes to emphasize. Understanding key signatures is fundamental for reading sheet music and performing accurately.