What is the purpose of a repeat sign in music?

The purpose of a repeat sign in music is to indicate that a specific section should be played again. This is typically represented by two dots placed either before a line or at the end, and it signals to the performer to return to a designated point in the music and repeat that passage. Repeat signs help create structure and reinforce musical ideas within a piece by encouraging certain passages to be emphasized through repetition.

In contrast, the other options serve different functions in music notation. A sign indicating the end of a piece is typically a double bar line or a specific closing symbol, which does not serve the purpose of repetition. Tempo changes are often marked with specific terms or symbols, such as "allegro" or "ritardando," that guide the performer on how fast or slow to play but do not involve repetitions of any section. Dynamics, which refer to the volume of music—like loud and soft—are indicated through symbols such as "p" for piano and "f" for forte, and they do not imply that any specific section of music should be played again.